diff --git a/lib/Serialization/SerializedModuleLoader.cpp b/lib/Serialization/SerializedModuleLoader.cpp
index 59e2d019faa1c..032b1f8c56623 100644
--- a/lib/Serialization/SerializedModuleLoader.cpp
+++ b/lib/Serialization/SerializedModuleLoader.cpp
@@ -49,14 +49,10 @@ void forEachTargetModuleBasename(const ASTContext &Ctx,
   // names checked in "#if arch(...)". Fall back to that name in the one case
   // where it's different from what Swift 4.2 supported:
   // - 32-bit ARM platforms (formerly "arm")
-  // - arm64e (formerly shared with "arm64")
   // We should be able to drop this once there's an Xcode that supports the
   // new names.
-  if (Ctx.LangOpts.Target.getArch() == llvm::Triple::ArchType::arm)
+  if (Ctx.LangOpts.Target.getArch() == llvm::Triple::ArchType::arm) {
     body("arm");
-  else if (Ctx.LangOpts.Target.getSubArch() ==
-           llvm::Triple::SubArchType::AArch64SubArch_E) {
-    body("arm64");
   }
 }
 
@@ -409,8 +405,12 @@ bool SerializedModuleLoader::maybeDiagnoseTargetMismatch(
       return false;
     StringRef filePath = directoryIterator->path();
     StringRef extension = llvm::sys::path::extension(filePath);
-    if (file_types::lookupTypeForExtension(extension) ==
-          file_types::TY_SwiftModuleFile) {
+    auto fileType = file_types::lookupTypeForExtension(extension);
+    // We also check for interfaces here, because the SerializedModuleLoader
+    // is invoked after the ModuleInterfaceLoader; if the ModuleInterfaceLoader
+    // handled interfaces separately, we could get duplicate diagnostics.
+    if (fileType == file_types::TY_SwiftModuleFile
+        || fileType == file_types::TY_SwiftModuleInterfaceFile) {
       if (!foundArchs.empty())
         foundArchs += ", ";
       foundArchs += llvm::sys::path::stem(filePath).str();
@@ -418,7 +418,7 @@ bool SerializedModuleLoader::maybeDiagnoseTargetMismatch(
   }
 
   if (foundArchs.empty()) {
-    // Maybe this swiftmodule directory only contains swiftinterfaces, or
+    // It is strange that there were no swiftmodules or swiftinterfaces here;
     // maybe something else is going on. Regardless, we shouldn't emit a
     // possibly incorrect diagnostic.
     return false;
diff --git a/test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64-apple-ios.swiftinterface b/test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64-apple-ios.swiftinterface
new file mode 100644
index 0000000000000..cf71c2f1a1e21
--- /dev/null
+++ b/test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64-apple-ios.swiftinterface
@@ -0,0 +1,4 @@
+// swift-interface-format-version: 1.0
+// swift-compiler-version: Apple Swift version 5.2
+// swift-module-flags: -target arm64-apple-ios13.0 -enable-library-evolution -swift-version 5 -module-name DummyFramework
+import Swift
diff --git a/test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64.swiftinterface b/test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64.swiftinterface
new file mode 100644
index 0000000000000..cf71c2f1a1e21
--- /dev/null
+++ b/test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64.swiftinterface
@@ -0,0 +1,4 @@
+// swift-interface-format-version: 1.0
+// swift-compiler-version: Apple Swift version 5.2
+// swift-module-flags: -target arm64-apple-ios13.0 -enable-library-evolution -swift-version 5 -module-name DummyFramework
+import Swift
diff --git a/test/ModuleInterface/ModuleCache/force-module-loading-mode-archs.swift b/test/ModuleInterface/ModuleCache/force-module-loading-mode-archs.swift
index 280b1a82aa273..34c87a5841a16 100644
--- a/test/ModuleInterface/ModuleCache/force-module-loading-mode-archs.swift
+++ b/test/ModuleInterface/ModuleCache/force-module-loading-mode-archs.swift
@@ -14,7 +14,7 @@
 // RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 // RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 // RUN: env SWIFT_FORCE_MODULE_LOADING=only-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
-// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH-2 -DARCH=%module-target-triple -DTARGET_CPU=%target-cpu %s
 // (default)
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -I %t %s 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 
@@ -82,19 +82,19 @@
 
 // 8. Only the interface is present but for the wrong architecture.
 // (Diagnostics for the module only are tested elsewhere.)
-// FIXME: We should improve this to not just say NO-SUCH-MODULE.
 // RUN: rm %t/Lib.swiftmodule/garbage.swiftmodule
-// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
-// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
 // RUN: env SWIFT_FORCE_MODULE_LOADING=only-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
-// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -I %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
 // (default)
-// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -I %t %s 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -I %t %s 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
 
 import Lib
 // NO-SUCH-MODULE: [[@LINE-1]]:8: error: no such module 'Lib'
 // BAD-MODULE: [[@LINE-2]]:8: error: malformed compiled module: {{.*}}Lib.swiftmodule
 // WRONG-ARCH: [[@LINE-3]]:8: error: could not find module 'Lib' for target '[[ARCH]]'; found: garbage
+// WRONG-ARCH-2: [[@LINE-4]]:8: error: could not find module 'Lib' for target '[[ARCH]]'; found: [[TARGET_CPU]]
 
 struct X {}
 let _: X = Lib.testValue
diff --git a/test/ModuleInterface/ModuleCache/force-module-loading-mode-framework.swift b/test/ModuleInterface/ModuleCache/force-module-loading-mode-framework.swift
index cd2a43d5f7fec..4722b6dfb3cfb 100644
--- a/test/ModuleInterface/ModuleCache/force-module-loading-mode-framework.swift
+++ b/test/ModuleInterface/ModuleCache/force-module-loading-mode-framework.swift
@@ -14,7 +14,7 @@
 // RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 // RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 // RUN: env SWIFT_FORCE_MODULE_LOADING=only-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
-// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH-2 -DARCH=%module-target-triple -DTARGET_CPU=%target-cpu %s
 // (default)
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -F %t %s 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
 
@@ -83,19 +83,19 @@
 
 // 8. Only the interface is present but for the wrong architecture.
 // (Diagnostics for the module only are tested elsewhere.)
-// FIXME: We should improve this to not just say NO-SUCH-MODULE.
 // RUN: rm %t/Lib.framework/Modules/Lib.swiftmodule/garbage.swiftmodule
-// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
-// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=prefer-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
 // RUN: env SWIFT_FORCE_MODULE_LOADING=only-parseable not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
-// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: env SWIFT_FORCE_MODULE_LOADING=only-serialized not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP %s -F %t 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
 // (default)
-// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -F %t %s 2>&1 | %FileCheck -check-prefix=NO-SUCH-MODULE %s
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -F %t %s 2>&1 | %FileCheck -check-prefix=WRONG-ARCH -DARCH=%module-target-triple %s
 
 import Lib
 // NO-SUCH-MODULE: [[@LINE-1]]:8: error: no such module 'Lib'
 // BAD-MODULE: [[@LINE-2]]:8: error: malformed compiled module: {{.*}}Lib.swiftmodule
 // WRONG-ARCH: [[@LINE-3]]:8: error: could not find module 'Lib' for target '[[ARCH]]'; found: garbage
+// WRONG-ARCH-2: [[@LINE-4]]:8: error: could not find module 'Lib' for target '[[ARCH]]'; found: [[TARGET_CPU]]
 
 struct X {}
 let _: X = Lib.testValue
diff --git a/test/ModuleInterface/arm64e-fallback.swift b/test/ModuleInterface/arm64e-fallback.swift
new file mode 100644
index 0000000000000..d60ccb5e6898c
--- /dev/null
+++ b/test/ModuleInterface/arm64e-fallback.swift
@@ -0,0 +1,6 @@
+// RUN: not %target-typecheck-verify-swift -target arm64e-apple-ios13.0 -F %S/Inputs 2>&1 | %FileCheck %s
+
+// REQUIRES: OS=ios
+
+import DummyFramework
+// CHECK: could not find module 'DummyFramework' for target 'arm64e-apple-ios'; found: arm64-apple-ios, arm64