diff --git a/lib/ClangImporter/ImportType.cpp b/lib/ClangImporter/ImportType.cpp
index aafb93ffd8b1b..0827c535af4a9 100644
--- a/lib/ClangImporter/ImportType.cpp
+++ b/lib/ClangImporter/ImportType.cpp
@@ -2439,6 +2439,15 @@ static bool isParameterContextGlobalActorIsolated(DeclContext *dc,
   return false;
 }
 
+static bool isSendableInferenceOnCompletionHandlerParameterAllowed(
+    DeclContext *dc, const clang::Decl *parent) {
+  auto &C = dc->getASTContext();
+  if (!C.LangOpts.hasFeature(Feature::SendableCompletionHandlers))
+    return false;
+
+  return !isParameterContextGlobalActorIsolated(dc, parent);
+}
+
 std::optional<ClangImporter::Implementation::ImportParameterTypeResult>
 ClangImporter::Implementation::importParameterType(
     DeclContext *dc, const clang::Decl *parent, const clang::ParmVarDecl *param,
@@ -2462,10 +2471,9 @@ ClangImporter::Implementation::importParameterType(
   bool isConsuming = false;
   bool isParamTypeImplicitlyUnwrapped = false;
 
-  if (SwiftContext.LangOpts.hasFeature(Feature::SendableCompletionHandlers) &&
-      paramIsCompletionHandler) {
-    if (!isParameterContextGlobalActorIsolated(dc, parent))
-      attrs |= ImportTypeAttr::DefaultsToSendable;
+  if (paramIsCompletionHandler &&
+      isSendableInferenceOnCompletionHandlerParameterAllowed(dc, parent)) {
+    attrs |= ImportTypeAttr::DefaultsToSendable;
   }
 
   if (auto optionSetEnum = importer::findOptionSetEnum(paramTy, *this)) {
@@ -3344,11 +3352,19 @@ ImportedType ClangImporter::Implementation::importMethodParamsAndReturnType(
               decomposeCompletionHandlerType(swiftParamTy, *asyncInfo)) {
         swiftResultTy = replacedSwiftResultTy;
 
+        ImportTypeAttrs attrs;
+        // This is required because a parameter type of a sync variant and
+        // a completion type of an async variant have to match exactly.
+        if (isSendableInferenceOnCompletionHandlerParameterAllowed(origDC,
+                                                                   clangDecl)) {
+          attrs |= ImportTypeAttr::DefaultsToSendable;
+        }
+
         // Import the original completion handler type without adjustments.
         Type origSwiftParamTy =
             importType(paramTy, ImportTypeKind::CompletionHandlerParameter,
                        paramAddDiag, allowNSUIntegerAsIntInParam,
-                       Bridgeability::Full, ImportTypeAttrs(),
+                       Bridgeability::Full, attrs,
                        optionalityOfParam,
                        /*resugarNSErrorPointer=*/!paramIsError, std::nullopt)
                 .getType();
diff --git a/test/ClangImporter/regionbasedisolation.swift b/test/ClangImporter/regionbasedisolation.swift
index 0f1529100e073..63a2364dafbb2 100644
--- a/test/ClangImporter/regionbasedisolation.swift
+++ b/test/ClangImporter/regionbasedisolation.swift
@@ -72,7 +72,7 @@ extension ObjCObject {
   // CHECK: [[RESULT:%.*]] = alloc_stack $Array<NSObject>
 
   // Our method.
-  // CHECK: [[METHOD:%.*]] = objc_method [[SELF]], #ObjCObject.loadObjects2!foreign : (ObjCObject) -> () async throws -> [NSObject], $@convention(objc_method) (@convention(block) (Optional<NSArray>, Optional<NSError>) -> (), ObjCObject) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method [[SELF]], #ObjCObject.loadObjects2!foreign : (ObjCObject) -> () async throws -> [NSObject], $@convention(objc_method) (@convention(block) @Sendable (Optional<NSArray>, Optional<NSError>) -> (), ObjCObject) -> ()
 
   // Begin setting up the unsafe continuation for our method. Importantly note
   // that [[UNSAFE_CONT]] is Sendable, so we lose any connection from the
@@ -101,17 +101,18 @@ extension ObjCObject {
   // CHECK: copy_addr [take] [[CHECKED_CONT]] to [init] [[EXISTENTIAL_BLOCK_STORAGE]]
   // CHECK: merge_isolation_region [[BLOCK_STORAGE]], [[RESULT]]
 
-  // Then create the actual block. NOTE: Since the block is not @Sendable, the block does propagate regions.
+  // Then create the actual block. NOTE: Since the block is @Sendable, the block
+  // does not propagate regions.
   //
-  // CHECK: [[COMPLETION_HANDLER_BLOCK:%.*]] = function_ref @$sSo7NSArrayCSgSo7NSErrorCSgIeyByy_SaySo8NSObjectCGTz_ : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSArray>, Optional<NSError>) -> ()
+  // CHECK: [[COMPLETION_HANDLER_BLOCK:%.*]] = function_ref @$sSo7NSArrayCSgSo7NSErrorCSgIeyBhyy_SaySo8NSObjectCGTz_ : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSArray>, Optional<NSError>) -> ()
   // CHECK: [[COMPLETION_BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]], invoke [[COMPLETION_HANDLER_BLOCK]]
   //
-  // Since the block is not @Sendable, it does propagate the connection in
+  // Since the block is @Sendable, it does not propagate the connection in
   // between self and the block storage when we just call the method. Thus we
-  // don't need to perform a merge_isolation_region to communicate that the block
+  // need to perform a merge_isolation_region to communicate that the block
   // storage and self are part of the same region.
   //
-  // CHECK-NOT: merge_isolation_region [[SELF]], [[BLOCK_STORAGE]]
+  // CHECK: merge_isolation_region [[SELF]], [[BLOCK_STORAGE]]
   //
   // Then call the method.
   // CHECK: apply [[METHOD]]([[COMPLETION_BLOCK]], [[SELF]])
diff --git a/test/SILGen/objc_async.swift b/test/SILGen/objc_async.swift
index f5012bc10d86c..bf6eb7a038823 100644
--- a/test/SILGen/objc_async.swift
+++ b/test/SILGen/objc_async.swift
@@ -10,14 +10,14 @@ func testSlowServer(slowServer: SlowServer) async throws {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $Int
   // CHECK: [[STRINGINIT:%.*]] = function_ref @$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF :
   // CHECK: [[ARG:%.*]] = apply [[STRINGINIT]]
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) (Int) -> (), SlowServer) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) @Sendable (Int) -> (), SlowServer) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr Int, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<Int, Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
   // CHECK: [[CONT_SLOT:%.*]] = project_block_storage [[BLOCK_STORAGE]]
   // CHECK: [[CONT_SLOT_ADDR:%.*]] = init_existential_addr [[CONT_SLOT]]
   // CHECK: store [[WRAPPED]] to [trivial] [[CONT_SLOT_ADDR]]
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Int) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Int) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[ARG]], [[BLOCK]], %0)
   // CHECK: [[COPY:%.*]] = copy_value [[ARG]]
@@ -33,14 +33,14 @@ func testSlowServer(slowServer: SlowServer) async throws {
   let _: Int = await slowServer.doSomethingSlowNullably("mail")
 
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $String
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) (Optional<NSString>, Optional<NSError>) -> (), SlowServer) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> (), SlowServer) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr [throws] String, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<String, any Error> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
   // CHECK: [[CONT_SLOT:%.*]] = project_block_storage [[BLOCK_STORAGE]]
   // CHECK: [[CONT_SLOT_ADDR:%.*]] = init_existential_addr [[CONT_SLOT]]
   // CHECK: store [[WRAPPED]] to [trivial] [[CONT_SLOT_ADDR]]
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[STRING_COMPLETION_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, Optional<NSError>) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[STRING_COMPLETION_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, Optional<NSError>) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[BLOCK]], %0)
   // CHECK: await_async_continuation [[CONT]] {{.*}}, resume [[RESUME:bb[0-9]+]], error [[ERROR:bb[0-9]+]]
@@ -50,18 +50,18 @@ func testSlowServer(slowServer: SlowServer) async throws {
   // CHECK: dealloc_stack [[RESUME_BUF]]
   let _: String = try await slowServer.findAnswer()
 
-  // CHECK: objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) () -> (), SlowServer) -> ()
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[VOID_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any) -> ()
+  // CHECK: objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) @Sendable () -> (), SlowServer) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[VOID_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any) -> ()
   await slowServer.serverRestart("somewhere")
 
-  // CHECK: function_ref @[[STRING_NONZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>) -> ()
+  // CHECK: function_ref @[[STRING_NONZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>) -> ()
   let _: String = try await slowServer.doSomethingFlaggy()
-  // CHECK: function_ref @[[STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, {{.*}}Bool, Optional<NSError>) -> ()
+  // CHECK: function_ref @[[STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, {{.*}}Bool, Optional<NSError>) -> ()
   let _: String = try await slowServer.doSomethingZeroFlaggy()
-  // CHECK: function_ref @[[STRING_STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>, Optional<NSString>) -> ()
+  // CHECK: function_ref @[[STRING_STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>, Optional<NSString>) -> ()
   let _: (String, String) = try await slowServer.doSomethingMultiResultFlaggy()
 
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSSTRING_INT_THROW_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, Int, Optional<NSError>) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSSTRING_INT_THROW_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, Int, Optional<NSError>) -> ()
   let (_, _): (String, Int) = try await slowServer.findMultipleAnswers()
 
   let (_, _): (Bool, Bool) = try await slowServer.findDifferentlyFlavoredBooleans()
@@ -189,14 +189,14 @@ func testSlowServerFromMain(slowServer: SlowServer) async throws {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $Int
   // CHECK: [[STRINGINIT:%.*]] = function_ref @$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF :
   // CHECK: [[ARG:%.*]] = apply [[STRINGINIT]]
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) (Int) -> (), SlowServer) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) @Sendable (Int) -> (), SlowServer) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr Int, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<Int, Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
   // CHECK: [[CONT_SLOT:%.*]] = project_block_storage [[BLOCK_STORAGE]]
   // CHECK: [[CONT_SLOT_ANY:%.*]] = init_existential_addr [[CONT_SLOT]]
   // CHECK: store [[WRAPPED]] to [trivial] [[CONT_SLOT_ANY]]
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Int) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Int) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[ARG]], [[BLOCK]], %0)
   // CHECK: [[COPY:%.*]] = copy_value [[ARG]]
@@ -223,10 +223,10 @@ func testThrowingMethodFromMain(slowServer: SlowServer) async -> String {
 // CHECK:  [[PROJECTED:%.*]] = project_block_storage [[STORE_ALLOC]] : $*@block_storage
 // CHECK:  [[PROJECTED_ANY:%.*]] = init_existential_addr [[PROJECTED]]
 // CHECK:  store [[CONT]] to [trivial] [[PROJECTED_ANY]]
-// CHECK:  [[INVOKER:%.*]] = function_ref @$sSo8NSStringCSgSo7NSErrorCSgIeyByy_SSTz_
+// CHECK:  [[INVOKER:%.*]] = function_ref @$sSo8NSStringCSgSo7NSErrorCSgIeyBhyy_SSTz_
 // CHECK:  [[BLOCK:%.*]] = init_block_storage_header [[STORE_ALLOC]] {{.*}}, invoke [[INVOKER]]
 // CHECK:  [[OPTIONAL_BLK:%.*]] = enum {{.*}}, #Optional.some!enumelt, [[BLOCK]]
-// CHECK:  apply [[METH]]([[STRING_ARG]], [[OPTIONAL_BLK]], {{%.*}}) : $@convention(objc_method) (NSString, Optional<@convention(block) (Optional<NSString>, Optional<NSError>) -> ()>, SlowServer) -> ()
+// CHECK:  apply [[METH]]([[STRING_ARG]], [[OPTIONAL_BLK]], {{%.*}}) : $@convention(objc_method) (NSString, Optional<@convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> ()>, SlowServer) -> ()
 // CHECK:  [[STRING_ARG_COPY:%.*]] = copy_value [[STRING_ARG]] : $NSString
 // CHECK:  dealloc_stack [[STORE_ALLOC]] : $*@block_storage Any
 // CHECK:  destroy_value [[STRING_ARG]] : $NSString
@@ -340,10 +340,10 @@ extension SlowServer: @retroactive FailableFloatLoader {
 }
 // CHECK-LABEL: sil [ossa] @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKF : $@convention(method) @async (@guaranteed SlowServer) -> (Float, @error any Error)
 
-// CHECK-LABEL: sil private [thunk] [ossa] @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKFTo : $@convention(objc_method) (@convention(block) (Float, Optional<NSError>) -> (), SlowServer) -> () {
+// CHECK-LABEL: sil private [thunk] [ossa] @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKFTo : $@convention(objc_method) (@convention(block) @Sendable (Float, Optional<NSError>) -> (), SlowServer) -> () {
 // CHECK:         function_ref @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKFyyYacfU_To
 
-// CHECK-LABEL: sil shared [thunk] [ossa] @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) (Float, Optional<NSError>) -> (), SlowServer) -> ()
+// CHECK-LABEL: sil shared [thunk] [ossa] @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) @Sendable (Float, Optional<NSError>) -> (), SlowServer) -> ()
 // CHECK:         [[BLOCK:%.*]] = copy_block
 // CHECK:         [[METHOD:%.*]] = function_ref @$sSo10SlowServerC10objc_asyncE16loadFloatOrThrowSfyYaKF :
 // CHECK:         try_apply [[METHOD]]({{%.*}}) : {{.*}}, normal bb1, error bb2
@@ -370,7 +370,7 @@ extension SlowServer: @retroactive FailableFloatLoader {
 // CHECK: [[SLOWSERVER_ANYOBJECT_M_B:%.*]] = begin_borrow [[SLOWSERVER_ANYOBJECT_M]]
 // CHECK: [[SLOWSERVER_ANYOBJECT_M_B_O:%.*]] = open_existential_ref [[SLOWSERVER_ANYOBJECT_M_B]]
 // CHECK: [[SLOWSERVER_ANYOBJECT_M_B_O_C:%.*]] = copy_value [[SLOWSERVER_ANYOBJECT_M_B_O]]
-// CHECK: [[METHOD:%.*]] = objc_method [[SLOWSERVER_ANYOBJECT_M_B_O_C]] : $@opened("{{.*}}", AnyObject) Self, #SlowServer.start!foreign : (SlowServer) -> (NSDate?) async -> (), $@convention(objc_method) (Optional<NSDate>, @convention(block) () -> (), @opened("{{.*}}", AnyObject) Self) -> ()
+// CHECK: [[METHOD:%.*]] = objc_method [[SLOWSERVER_ANYOBJECT_M_B_O_C]] : $@opened("{{.*}}", AnyObject) Self, #SlowServer.start!foreign : (SlowServer) -> (NSDate?) async -> (), $@convention(objc_method) (Optional<NSDate>, @convention(block) @Sendable () -> (), @opened("{{.*}}", AnyObject) Self) -> ()
 // CHECK: [[CONT:%.*]] = get_async_continuation_addr ()
 // CHECK: [[UNSAFE_CONT:%.*]] = struct $UnsafeContinuation<(), Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
 // CHECK: [[BLOCK:%.*]] = alloc_stack $@block_storage Any
@@ -378,9 +378,9 @@ extension SlowServer: @retroactive FailableFloatLoader {
 // CHECK: [[BLOCK_PROJECT_EX:%.*]] = init_existential_addr [[BLOCK_PROJECT]]
 // CHECK: store [[UNSAFE_CONT]] to [trivial] [[BLOCK_PROJECT_EX]]
 // CHECK: merge_isolation_region [[BLOCK]] : $*@block_storage Any,
-// CHECK: [[CONT_HANDLER:%.*]] = function_ref @$sIeyB_ytTz_ : $@convention(c) (@inout_aliasable @block_storage Any) -> ()
+// CHECK: [[CONT_HANDLER:%.*]] = function_ref @$sIeyBh_ytTz_ : $@convention(c) @Sendable (@inout_aliasable @block_storage Any) -> ()
 // CHECK: [[INIT_BLOCK_STORAGE_HEADER:%.*]] = init_block_storage_header [[BLOCK]] : $*@block_storage Any, invoke [[CONT_HANDLER]]
-// CHECK-NOT: merge_isolation_region [[SLOWSERVER_ANYOBJECT_M_B_O_C]] : $@opened("{{.*}}", AnyObject) Self, [[BLOCK]]
+// CHECK: merge_isolation_region [[SLOWSERVER_ANYOBJECT_M_B_O_C]] : $@opened("{{.*}}", AnyObject) Self, [[BLOCK]]
 // CHECK: apply [[METHOD]]({{%.*}}, [[INIT_BLOCK_STORAGE_HEADER]], [[SLOWSERVER_ANYOBJECT_M_B_O_C]])
 // CHECK: await_async_continuation [[CONT]] : $Builtin.RawUnsafeContinuation, resume bb1
 // CHECK: } // end sil function '$s10objc_async13testAnyObjectyySo10SlowServerCYaF'
diff --git a/test/SILGen/objc_async_checked.swift b/test/SILGen/objc_async_checked.swift
index 05e45c4345592..d716256c1b974 100644
--- a/test/SILGen/objc_async_checked.swift
+++ b/test/SILGen/objc_async_checked.swift
@@ -11,7 +11,7 @@ func testSlowServer(slowServer: SlowServer) async throws {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $Int
   // CHECK: [[STRINGINIT:%.*]] = function_ref @$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF :
   // CHECK: [[ARG:%.*]] = apply [[STRINGINIT]]
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) (Int) -> (), SlowServer) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) @Sendable (Int) -> (), SlowServer) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr Int, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<Int, Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
@@ -21,7 +21,7 @@ func testSlowServer(slowServer: SlowServer) async throws {
   // CHECK: [[CHECKED_CONT:%.*]] = alloc_stack $CheckedContinuation<Int, Never>
   // CHECK: {{.*}} = apply [[CHECKED_CONT_INIT_FN]]<Int>([[CHECKED_CONT]], [[WRAPPED]]) : $@convention(thin) <τ_0_0> (UnsafeContinuation<τ_0_0, Never>) -> @out CheckedContinuation<τ_0_0, Never>
   // CHECK: copy_addr [take] [[CHECKED_CONT]] to [init] [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<Int, Never>
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Int) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Int) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[ARG]], [[BLOCK]], %0)
   // CHECK: [[COPY:%.*]] = copy_value [[ARG]]
@@ -40,7 +40,7 @@ func testSlowServer(slowServer: SlowServer) async throws {
   let _: Int = await slowServer.doSomethingSlowNullably("mail")
 
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $String
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) (Optional<NSString>, Optional<NSError>) -> (), SlowServer) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> (), SlowServer) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr [throws] String, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<String, any Error> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
@@ -50,7 +50,7 @@ func testSlowServer(slowServer: SlowServer) async throws {
   // CHECK: [[CHECKED_CONT:%.*]] = alloc_stack $CheckedContinuation<String, any Error>
   // CHECK: {{.*}} = apply [[CHECKED_CONT_INIT_FN]]<String>([[CHECKED_CONT]], [[WRAPPED]]) : $@convention(thin) <τ_0_0> (UnsafeContinuation<τ_0_0, any Error>) -> @out CheckedContinuation<τ_0_0, any Error>
   // CHECK: copy_addr [take] [[CHECKED_CONT]] to [init] [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<String, any Error>
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[STRING_COMPLETION_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, Optional<NSError>) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[STRING_COMPLETION_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, Optional<NSError>) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[BLOCK]], %0)
   // CHECK: destroy_addr [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<String, any Error>
@@ -62,18 +62,18 @@ func testSlowServer(slowServer: SlowServer) async throws {
   // CHECK: dealloc_stack [[RESUME_BUF]]
   let _: String = try await slowServer.findAnswer()
 
-  // CHECK: objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) () -> (), SlowServer) -> ()
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[VOID_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any) -> ()
+  // CHECK: objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) @Sendable () -> (), SlowServer) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[VOID_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any) -> ()
   await slowServer.serverRestart("somewhere")
 
-  // CHECK: function_ref @[[STRING_NONZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>) -> ()
+  // CHECK: function_ref @[[STRING_NONZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>) -> ()
   let _: String = try await slowServer.doSomethingFlaggy()
-  // CHECK: function_ref @[[STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, {{.*}}Bool, Optional<NSError>) -> ()
+  // CHECK: function_ref @[[STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, {{.*}}Bool, Optional<NSError>) -> ()
   let _: String = try await slowServer.doSomethingZeroFlaggy()
-  // CHECK: function_ref @[[STRING_STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>, Optional<NSString>) -> ()
+  // CHECK: function_ref @[[STRING_STRING_ZERO_FLAG_THROW_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, {{.*}}Bool, Optional<NSString>, Optional<NSError>, Optional<NSString>) -> ()
   let _: (String, String) = try await slowServer.doSomethingMultiResultFlaggy()
 
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSSTRING_INT_THROW_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, Int, Optional<NSError>) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSSTRING_INT_THROW_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, Int, Optional<NSError>) -> ()
   let (_, _): (String, Int) = try await slowServer.findMultipleAnswers()
 
   let (_, _): (Bool, Bool) = try await slowServer.findDifferentlyFlavoredBooleans()
@@ -198,7 +198,7 @@ func testSlowServerFromMain(slowServer: SlowServer) async throws {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $Int
   // CHECK: [[STRINGINIT:%.*]] = function_ref @$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF :
   // CHECK: [[ARG:%.*]] = apply [[STRINGINIT]]
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) (Int) -> (), SlowServer) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (NSString, @convention(block) @Sendable (Int) -> (), SlowServer) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr Int, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<Int, Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
@@ -208,7 +208,7 @@ func testSlowServerFromMain(slowServer: SlowServer) async throws {
   // CHECK: [[CHECKED_CONT:%.*]] = alloc_stack $CheckedContinuation<Int, Never>
   // CHECK: {{.*}} = apply [[CHECKED_CONT_INIT_FN]]<Int>([[CHECKED_CONT]], [[WRAPPED]]) : $@convention(thin) <τ_0_0> (UnsafeContinuation<τ_0_0, Never>) -> @out CheckedContinuation<τ_0_0, Never>
   // CHECK: copy_addr [take] [[CHECKED_CONT]] to [init] [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<Int, Never>
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Int) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[INT_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Int) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[ARG]], [[BLOCK]], %0)
   // CHECK: [[COPY:%.*]] = copy_value [[ARG]]
@@ -229,7 +229,7 @@ func testSlowServerFromMain(slowServer: SlowServer) async throws {
 // CHECK: [[STR:%.*]] = alloc_stack $String
 // CHECK: [[ERR:%.*]] = alloc_stack [dynamic_lifetime] $Optional<NSError>
 // CHECK: inject_enum_addr [[ERR]] : $*Optional<NSError>, #Optional.none!enumelt
-// CHECK: [[METHOD:%.*]] = objc_method %0 : $SlowServer, #SlowServer.findAnswerFailingly!foreign : (SlowServer) -> () async throws -> String, $@convention(objc_method) (Optional<AutoreleasingUnsafeMutablePointer<Optional<NSError>>>, @convention(block) (Optional<NSString>, Optional<NSError>) -> (), SlowServer) -> ObjCBool
+// CHECK: [[METHOD:%.*]] = objc_method %0 : $SlowServer, #SlowServer.findAnswerFailingly!foreign : (SlowServer) -> () async throws -> String, $@convention(objc_method) (Optional<AutoreleasingUnsafeMutablePointer<Optional<NSError>>>, @convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> (), SlowServer) -> ObjCBool
 // CHECK: [[RAW_CONT:%.*]] = get_async_continuation_addr [throws] String, {{.*}} : $*String
 // CHECK: [[UNSAFE_CONT:%.*]] = struct $UnsafeContinuation<String, any Error> ([[RAW_CONT]] : $Builtin.RawUnsafeContinuation)
 // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
@@ -272,10 +272,10 @@ func testThrowingMethodFromMain(slowServer: SlowServer) async -> String {
 // CHECK:  [[CHECKED_CONT:%.*]] = alloc_stack $CheckedContinuation<String, any Error>
 // CHECK:  {{.*}} = apply [[CHECKED_CONT_INIT_FN]]<String>([[CHECKED_CONT]], [[CONT]]) : $@convention(thin) <τ_0_0> (UnsafeContinuation<τ_0_0, any Error>) -> @out CheckedContinuation<τ_0_0, any Error>
 // CHECK:  copy_addr [take] [[CHECKED_CONT]] to [init] [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<String, any Error>
-// CHECK:  [[INVOKER:%.*]] = function_ref @$sSo8NSStringCSgSo7NSErrorCSgIeyByy_SSTz_
+// CHECK:  [[INVOKER:%.*]] = function_ref @$sSo8NSStringCSgSo7NSErrorCSgIeyBhyy_SSTz_
 // CHECK:  [[BLOCK:%.*]] = init_block_storage_header [[STORE_ALLOC]] {{.*}}, invoke [[INVOKER]]
 // CHECK:  [[OPTIONAL_BLK:%.*]] = enum {{.*}}, #Optional.some!enumelt, [[BLOCK]]
-// CHECK:  {{.*}} = apply [[METH]]([[STRING_ARG]], [[OPTIONAL_BLK]], {{%.*}}) : $@convention(objc_method) (NSString, Optional<@convention(block) (Optional<NSString>, Optional<NSError>) -> ()>, SlowServer) -> ()
+// CHECK:  {{.*}} = apply [[METH]]([[STRING_ARG]], [[OPTIONAL_BLK]], {{%.*}}) : $@convention(objc_method) (NSString, Optional<@convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> ()>, SlowServer) -> ()
 // CHECK:  [[STRING_ARG_COPY:%.*]] = copy_value [[STRING_ARG]] : $NSString
 // CHECK:  destroy_addr [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<String, any Error>
 // CHECK:  dealloc_stack [[CHECKED_CONT]] : $*CheckedContinuation<String, any Error>
diff --git a/test/SILGen/objc_async_from_swift.swift b/test/SILGen/objc_async_from_swift.swift
index 9497397c16592..63e6f97efa4e7 100644
--- a/test/SILGen/objc_async_from_swift.swift
+++ b/test/SILGen/objc_async_from_swift.swift
@@ -136,7 +136,7 @@ class SlowServerlet: SlowServer {
     //
     // @objc thunk closure
     //
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC011doSomethingE8NullablyySiSSYaFyyYacfU_To : $@convention(thin) @Sendable @async (NSString, Optional<@convention(block) (Int) -> ()>, SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC011doSomethingE8NullablyySiSSYaFyyYacfU_To : $@convention(thin) @Sendable @async (NSString, Optional<@convention(block) @Sendable (Int) -> ()>, SlowServerlet) -> () {
     // CHECK-NN: [[NONE:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK: [[STR_ARG:%.*]] = begin_borrow {{.*}} : $String
     // CHECK: [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
@@ -163,7 +163,7 @@ class SlowServerlet: SlowServer {
     // CHECK-NN: } // end sil function '$s21objc_async_from_swift13SlowServerletC18findAnswerNullablyyS2SYaF'
 
     // @objc closure thunk
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC18findAnswerNullablyyS2SYaFyyYacfU_To : $@convention(thin) @Sendable @async (NSString, Optional<@convention(block) (NSString) -> ()>, SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC18findAnswerNullablyyS2SYaFyyYacfU_To : $@convention(thin) @Sendable @async (NSString, Optional<@convention(block) @Sendable (NSString) -> ()>, SlowServerlet) -> () {
     // CHECK-NN: [[ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK: [[STR_ARG:%.*]] = begin_borrow {{.*}} : $String
     // CHECK: [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
@@ -191,7 +191,7 @@ class SlowServerlet: SlowServer {
 
     // @objc thunk closure
     //
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC28doSomethingDangerousNullablyyS2SYaKFyyYacfU_To : $@convention(thin) @Sendable @async (NSString, Optional<@convention(block) (Optional<NSString>, Optional<NSError>) -> ()>, SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC28doSomethingDangerousNullablyyS2SYaKFyyYacfU_To : $@convention(thin) @Sendable @async (NSString, Optional<@convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> ()>, SlowServerlet) -> () {
     // CHECK-NN: [[ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK: [[STR_ARG:%.*]] = begin_borrow {{.*}} : $String
     // CHECK: [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
@@ -218,7 +218,7 @@ class SlowServerlet: SlowServer {
     // CHECK-NN: } // end sil function '$s21objc_async_from_swift13SlowServerletC30doSomethingUnspecifiedNullablySSyYaKF'
 
     // @objc closure thunk
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC30doSomethingUnspecifiedNullablySSyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (Optional<@convention(block) (Optional<NSString>, Optional<NSError>) -> ()>, SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC30doSomethingUnspecifiedNullablySSyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (Optional<@convention(block) @Sendable (Optional<NSString>, Optional<NSError>) -> ()>, SlowServerlet) -> () {
     // CHECK-NN: [[ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK: [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
     // CHECK-C: [[NATIVE:%.*]] = function_ref @$s21objc_async_from_swift13SlowServerletC30doSomethingUnspecifiedNullablySSyYaKF : $@convention(method) @async (@guaranteed SlowServerlet) -> (@owned String, @error any Error)
@@ -244,7 +244,7 @@ class SlowServerlet: SlowServer {
     // CHECK-NN: } // end sil function '$s21objc_async_from_swift13SlowServerletC17doSomethingFlaggySSyYaKF'
 
     // @objc thunk closure
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC17doSomethingFlaggySSyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) ({{.*}}, Optional<NSString>, Optional<NSError>) -> (), SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC17doSomethingFlaggySSyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) @Sendable ({{.*}}, Optional<NSString>, Optional<NSError>) -> (), SlowServerlet) -> () {
     // CHECK-NN: [[ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK:    [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
     // CHECK-C:  [[NATIVE:%.*]] = function_ref @$s21objc_async_from_swift13SlowServerletC17doSomethingFlaggySSyYaKF : $@convention(method) @async (@guaranteed SlowServerlet) -> (@owned String, @error any Error)
@@ -276,7 +276,7 @@ class SlowServerlet: SlowServer {
     // CHECK-NN: } // end sil function '$s21objc_async_from_swift13SlowServerletC21doSomethingZeroFlaggySSyYaKF'
     //
     // @objc thunk closure
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC21doSomethingZeroFlaggySSyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) (Optional<NSString>, {{.*}}, Optional<NSError>) -> (), SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC21doSomethingZeroFlaggySSyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) @Sendable (Optional<NSString>, {{.*}}, Optional<NSError>) -> (), SlowServerlet) -> () {
     // CHECK-NN:   [[ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK:      [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
     // CHECK-C:    [[NATIVE:%.*]] = function_ref @$s21objc_async_from_swift13SlowServerletC21doSomethingZeroFlaggySSyYaKF : $@convention(method) @async (@guaranteed SlowServerlet) -> (@owned String, @error any Error)
@@ -306,7 +306,7 @@ class SlowServerlet: SlowServer {
     // CHECK-NN:   hop_to_executor [[ACTOR]]
     // CHECK-NN: } // end sil function '$s21objc_async_from_swift13SlowServerletC28doSomethingMultiResultFlaggySS_SStyYaKF'
     //
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC28doSomethingMultiResultFlaggySS_SStyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) ({{.*}}, Optional<NSString>, Optional<NSError>, Optional<NSString>) -> (), SlowServerlet) -> () {
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s21objc_async_from_swift13SlowServerletC28doSomethingMultiResultFlaggySS_SStyYaKFyyYacfU_To : $@convention(thin) @Sendable @async (@convention(block) @Sendable ({{.*}}, Optional<NSString>, Optional<NSError>, Optional<NSString>) -> (), SlowServerlet) -> () {
     // CHECK-NN: [[ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.none!enumelt
     // CHECK:    [[SELF:%.*]] = begin_borrow {{.*}} : $SlowServerlet
     // CHECK-C:  [[NATIVE:%.*]] = function_ref @$s21objc_async_from_swift13SlowServerletC28doSomethingMultiResultFlaggySS_SStyYaKF : $@convention(method) @async (@guaranteed SlowServerlet) -> (@owned String, @owned String, @error any Error)
@@ -436,8 +436,9 @@ func testAutoclosureInStaticMethod() {
     // CHECK:   [[INIT_PROJ_BLOCK_STORAGE:%.*]] = init_existential_addr [[PROJ_BLOCK_STORAGE]]
     // CHECK:   store [[UNSAFE_CONT]] to [trivial] [[INIT_PROJ_BLOCK_STORAGE]]
     // CHECK:   merge_isolation_region [[BLOCK_STORAGE]] : $*@block_storage Any, [[RESULT]]
-    // CHECK:   [[OBJC_COMPLETION_HANDLER_IMPL:%.*]] = function_ref @$sSo8NSStringCSgSo7NSErrorCSgIeyByy_SSTz_ : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSString>, Optional<NSError>) -> ()
+    // CHECK:   [[OBJC_COMPLETION_HANDLER_IMPL:%.*]] = function_ref @$sSo8NSStringCSgSo7NSErrorCSgIeyBhyy_SSTz_ : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSString>, Optional<NSError>) -> ()
     // CHECK:   [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] : $*@block_storage Any, invoke [[OBJC_COMPLETION_HANDLER_IMPL]]
+    // CHECK:   merge_isolation_region [[CAPTURE]] : $SlowServer, [[BLOCK_STORAGE]]
     // CHECK:   apply [[OBJC_METHOD]]([[NS_STRING]], [[BLOCK]], [[CAPTURE]])
     // CHECK:   await_async_continuation [[RAW_UNSAFE_CONT]] : $Builtin.RawUnsafeContinuation, resume [[RESUME_BB:bb[0-9]+]], error [[ERROR_BB:bb[0-9]+]]
     //
diff --git a/test/SILGen/objc_async_sendable_completion_handlers.swift b/test/SILGen/objc_async_sendable_completion_handlers.swift
new file mode 100644
index 0000000000000..fa9d5a15f2c4a
--- /dev/null
+++ b/test/SILGen/objc_async_sendable_completion_handlers.swift
@@ -0,0 +1,37 @@
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-sil %t/src/main.swift \
+// RUN:   -import-objc-header %t/src/Test.h \
+// RUN:   -swift-version 6 \
+// RUN:   -module-name main -I %t -verify | %FileCheck %t/src/main.swift
+
+// REQUIRES: objc_interop
+
+// rdar://154695053
+
+//--- Test.h
+
+@import Foundation;
+
+@interface Test <NSObject>
++(void) compute: (void (^)(void)) completion;
+@end
+
+//--- main.swift
+
+func test(v: Test.Type) async {
+  _ = await v.compute()
+}
+
+// CHECK-LABEL: sil hidden @$s4main4test1vySo4TestCm_tYaF : $@convention(thin) @async (@thick Test.Type) -> ()
+// CHECK: [[TEST_TYPE:%.*]] = thick_to_objc_metatype %0 to $@objc_metatype Test.Type
+// CHECK: [[METHOD:%.*]] = objc_method %5, #Test.compute!foreign : (Test.Type) -> () async -> (), $@convention(objc_method) (Optional<@convention(block) @Sendable () -> ()>, @objc_metatype Test.Type) -> ()
+// CHECK: [[BLOCK:%.*]] = alloc_stack $@block_storage Any
+// CHECK: [[COMPLETION_HANDLER:%.*]] = function_ref @$sIeyBh_ytTz_ : $@convention(c) @Sendable (@inout_aliasable @block_storage Any) -> ()
+// CHECK: [[HEADER:%.*]] = init_block_storage_header [[BLOCK]], invoke [[COMPLETION_HANDLER]]
+// CHECK: [[OPTIONAL_HEADER:%.*]] = enum $Optional<@convention(block) @Sendable () -> ()>, #Optional.some!enumelt, [[HEADER]]
+// CHECK: {{.*}} = apply [[METHOD]]([[OPTIONAL_HEADER]], [[TEST_TYPE]])
+// CHECK: } // end sil function '$s4main4test1vySo4TestCm_tYaF'
+
+// CHECK-LABEL: sil shared [transparent] [thunk] @$sIeyBh_ytTz_ : $@convention(c) @Sendable (@inout_aliasable @block_storage Any) -> ()
diff --git a/test/SILGen/objc_effectful_properties.swift b/test/SILGen/objc_effectful_properties.swift
index 6f60a8941e832..24dba591ecfae 100644
--- a/test/SILGen/objc_effectful_properties.swift
+++ b/test/SILGen/objc_effectful_properties.swift
@@ -8,14 +8,14 @@ import EffectfulProperties
 // CHECK-LABEL: sil {{.*}}@${{.*}}13testJustAsync
 func testJustAsync(eff : EffProps) async {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $NSObject
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) (NSObject) -> (), EffProps) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) @Sendable (NSObject) -> (), EffProps) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr NSObject, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<NSObject, Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
   // CHECK: [[CONT_SLOT:%.*]] = project_block_storage [[BLOCK_STORAGE]]
   // CHECK: [[CONT_SLOT_ADDR:%.*]] = init_existential_addr [[CONT_SLOT]]
   // CHECK: store [[WRAPPED]] to [trivial] [[CONT_SLOT_ADDR]]
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, NSObject) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, NSObject) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[BLOCK]], %0)
   // CHECK: await_async_continuation [[CONT]] {{.*}}, resume [[RESUME:bb[0-9]+]]
@@ -29,14 +29,14 @@ func testJustAsync(eff : EffProps) async {
 // CHECK-LABEL: sil {{.*}}@${{.*}}15testAsyncThrows
 func testAsyncThrows(eff : EffProps) async {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $Optional<NSObject>
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) (Optional<NSObject>, Optional<NSError>) -> (), EffProps) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) @Sendable (Optional<NSObject>, Optional<NSError>) -> (), EffProps) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr [throws] Optional<NSObject>, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<Optional<NSObject>, any Error> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
   // CHECK: [[CONT_SLOT:%.*]] = project_block_storage [[BLOCK_STORAGE]]
   // CHECK: [[CONT_SLOT_ADDR:%.*]] = init_existential_addr [[CONT_SLOT]]
   // CHECK: store [[WRAPPED]] to [trivial] [[CONT_SLOT_ADDR]]
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSObject>, Optional<NSError>) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSObject>, Optional<NSError>) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[BLOCK]], %0)
   // CHECK: await_async_continuation [[CONT]] {{.*}}, resume [[RESUME:bb[0-9]+]], error [[RESUME_ERROR:bb[0-9]+]]
diff --git a/test/SILGen/objc_effectful_properties_checked.swift b/test/SILGen/objc_effectful_properties_checked.swift
index 79fa319daff5b..14f891b76b69c 100644
--- a/test/SILGen/objc_effectful_properties_checked.swift
+++ b/test/SILGen/objc_effectful_properties_checked.swift
@@ -8,7 +8,7 @@ import EffectfulProperties
 // CHECK-LABEL: sil {{.*}}@${{.*}}13testJustAsync
 func testJustAsync(eff : EffProps) async {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $NSObject
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) (NSObject) -> (), EffProps) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) @Sendable (NSObject) -> (), EffProps) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr NSObject, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<NSObject, Never> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
@@ -18,7 +18,7 @@ func testJustAsync(eff : EffProps) async {
   // CHECK: [[CHECKED_CONT:%.*]] = alloc_stack $CheckedContinuation<NSObject, Never>
   // CHECK: {{.*}} = apply [[CHECKED_CONT_INIT_FN]]<NSObject>([[CHECKED_CONT]], [[WRAPPED]]) : $@convention(thin) <τ_0_0> (UnsafeContinuation<τ_0_0, Never>) -> @out CheckedContinuation<τ_0_0, Never>
   // CHECK: copy_addr [take] [[CHECKED_CONT]] to [init] [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<NSObject, Never>
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, NSObject) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, NSObject) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[BLOCK]], %0)
   // CHECK: destroy_addr [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<NSObject, Never>
@@ -34,7 +34,7 @@ func testJustAsync(eff : EffProps) async {
 // CHECK-LABEL: sil {{.*}}@${{.*}}15testAsyncThrows
 func testAsyncThrows(eff : EffProps) async {
   // CHECK: [[RESUME_BUF:%.*]] = alloc_stack $Optional<NSObject>
-  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) (Optional<NSObject>, Optional<NSError>) -> (), EffProps) -> ()
+  // CHECK: [[METHOD:%.*]] = objc_method {{.*}} $@convention(objc_method) (@convention(block) @Sendable (Optional<NSObject>, Optional<NSError>) -> (), EffProps) -> ()
   // CHECK: [[CONT:%.*]] = get_async_continuation_addr [throws] Optional<NSObject>, [[RESUME_BUF]]
   // CHECK: [[WRAPPED:%.*]] = struct $UnsafeContinuation<Optional<NSObject>, any Error> ([[CONT]] : $Builtin.RawUnsafeContinuation)
   // CHECK: [[BLOCK_STORAGE:%.*]] = alloc_stack $@block_storage Any
@@ -44,7 +44,7 @@ func testAsyncThrows(eff : EffProps) async {
   // CHECK: [[CHECKED_CONT:%.*]] = alloc_stack $CheckedContinuation<Optional<NSObject>, any Error>
   // CHECK: {{.*}} = apply [[CHECKED_CONT_INIT_FN:%.*]]<Optional<NSObject>>([[CHECKED_CONT]], [[WRAPPED]]) : $@convention(thin) <τ_0_0> (UnsafeContinuation<τ_0_0, any Error>) -> @out CheckedContinuation<τ_0_0, any Error>
   // CHECK: copy_addr [take] [[CHECKED_CONT]] to [init] [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<Optional<NSObject>, any Error>
-  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) (@inout_aliasable @block_storage Any, Optional<NSObject>, Optional<NSError>) -> ()
+  // CHECK: [[BLOCK_IMPL:%.*]] = function_ref @[[NSO_COMPLETION_BLOCK:.*]] : $@convention(c) @Sendable (@inout_aliasable @block_storage Any, Optional<NSObject>, Optional<NSError>) -> ()
   // CHECK: [[BLOCK:%.*]] = init_block_storage_header [[BLOCK_STORAGE]] {{.*}}, invoke [[BLOCK_IMPL]]
   // CHECK: apply [[METHOD]]([[BLOCK]], %0)
   // CHECK: destroy_addr [[CHECKED_CONT_SLOT]] : $*CheckedContinuation<Optional<NSObject>, any Error>