diff --git a/include/swift/AST/SubstitutionMap.h b/include/swift/AST/SubstitutionMap.h
index 1610d99d1f36..c536bd24ccd2 100644
--- a/include/swift/AST/SubstitutionMap.h
+++ b/include/swift/AST/SubstitutionMap.h
@@ -168,7 +168,7 @@ class SubstitutionMap {
 
   /// Query whether any replacement types in the map contain an opened
   /// existential.
-  bool hasOpenedExistential() const;
+  bool hasLocalArchetypes() const;
 
   /// Query whether any replacement types in the map contain dynamic Self.
   bool hasDynamicSelf() const;
diff --git a/include/swift/SIL/SILCloner.h b/include/swift/SIL/SILCloner.h
index de196c9befd4..c1ff1d715bd5 100644
--- a/include/swift/SIL/SILCloner.h
+++ b/include/swift/SIL/SILCloner.h
@@ -192,15 +192,11 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
     // If we have local archetypes to substitute, check whether that's
     // relevant to this particular substitution.
     if (!LocalArchetypeSubs.empty()) {
-      for (auto ty : Subs.getReplacementTypes()) {
+      if (Subs.hasLocalArchetypes()) {
         // If we found a type containing a local archetype, substitute
         // open existentials throughout the substitution map.
-        if (ty->hasLocalArchetype()) {
-          Subs = Subs.subst(QueryTypeSubstitutionMapOrIdentity{
-                              LocalArchetypeSubs},
-                            MakeAbstractConformanceForGenericType());
-          break;
-        }
+        Subs = Subs.subst(QueryTypeSubstitutionMapOrIdentity{LocalArchetypeSubs},
+                          MakeAbstractConformanceForGenericType());
       }
     }
 
@@ -223,7 +219,8 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
     return Ty.subst(
       Builder.getModule(),
       QueryTypeSubstitutionMapOrIdentity{LocalArchetypeSubs},
-      MakeAbstractConformanceForGenericType());
+      MakeAbstractConformanceForGenericType(),
+      CanGenericSignature());
   }
   SILType getOpType(SILType Ty) {
     Ty = getTypeInClonedContext(Ty);
diff --git a/lib/AST/ASTMangler.cpp b/lib/AST/ASTMangler.cpp
index a0974f588ec4..fe6dcac73a0e 100644
--- a/lib/AST/ASTMangler.cpp
+++ b/lib/AST/ASTMangler.cpp
@@ -653,13 +653,14 @@ std::string ASTMangler::mangleAutoDiffGeneratedDeclaration(
 static Type getTypeForDWARFMangling(Type t) {
   return t.subst(
     [](SubstitutableType *t) -> Type {
-      if (isa<GenericTypeParamType>(t))
-        return t->getCanonicalType();
-      return t;
+      if (isa<GenericTypeParamType>(t) &&
+          cast<GenericTypeParamType>(t)->isParameterPack()) {
+        return PackType::getSingletonPackExpansion(t->getCanonicalType());
+      }
+      return t->getCanonicalType();
     },
     MakeAbstractConformanceForGenericType(),
-    SubstFlags::AllowLoweredTypes |
-    SubstFlags::PreservePackExpansionLevel);
+    SubstFlags::AllowLoweredTypes);
 }
 
 std::string ASTMangler::mangleTypeForDebugger(Type Ty, GenericSignature sig) {
diff --git a/lib/AST/RequirementEnvironment.cpp b/lib/AST/RequirementEnvironment.cpp
index 7fea90446c54..68199b37a865 100644
--- a/lib/AST/RequirementEnvironment.cpp
+++ b/lib/AST/RequirementEnvironment.cpp
@@ -43,6 +43,13 @@ RequirementEnvironment::RequirementEnvironment(
   auto concreteType = conformanceDC->getSelfInterfaceType();
   auto conformanceSig = conformanceDC->getGenericSignatureOfContext();
 
+  auto conformanceToWitnessThunkGenericParamFn = [&](GenericTypeParamType *genericParam)
+      -> GenericTypeParamType * {
+    return GenericTypeParamType::get(genericParam->isParameterPack(),
+                                     genericParam->getDepth() + (covariantSelf ? 1 : 0),
+                                     genericParam->getIndex(), ctx);
+  };
+
   // This is a substitution function from the generic parameters of the
   // conforming type to the witness thunk environment.
   //
@@ -53,25 +60,20 @@ RequirementEnvironment::RequirementEnvironment(
   // This is a raw function rather than a substitution map because we need to
   // keep generic parameters as generic, even if the conformanceSig (the best
   // way to create the substitution map) equates them to concrete types.
-  auto conformanceToWitnessThunkTypeFn = [&](SubstitutableType *type) {
+  auto conformanceToWitnessThunkTypeFn = [&](SubstitutableType *type) -> Type {
     auto *genericParam = cast<GenericTypeParamType>(type);
-    if (covariantSelf) {
-      return GenericTypeParamType::get(genericParam->isParameterPack(),
-                                       genericParam->getDepth() + 1,
-                                       genericParam->getIndex(), ctx);
-    }
+    auto t = conformanceToWitnessThunkGenericParamFn(genericParam);
+    if (t->isParameterPack())
+      return PackType::getSingletonPackExpansion(t);
 
-    return GenericTypeParamType::get(genericParam->isParameterPack(),
-                                     genericParam->getDepth(),
-                                     genericParam->getIndex(), ctx);
+    return t;
   };
   auto conformanceToWitnessThunkConformanceFn =
       MakeAbstractConformanceForGenericType();
 
   auto substConcreteType = concreteType.subst(
       conformanceToWitnessThunkTypeFn,
-      conformanceToWitnessThunkConformanceFn,
-      SubstFlags::PreservePackExpansionLevel);
+      conformanceToWitnessThunkConformanceFn);
 
   // Calculate the depth at which the requirement's generic parameters
   // appear in the witness thunk signature.
@@ -168,9 +170,8 @@ RequirementEnvironment::RequirementEnvironment(
   // Now, add all generic parameters from the conforming type.
   if (conformanceSig) {
     for (auto param : conformanceSig.getGenericParams()) {
-      auto substParam = Type(param).subst(conformanceToWitnessThunkTypeFn,
-                                          conformanceToWitnessThunkConformanceFn);
-      genericParamTypes.push_back(substParam->castTo<GenericTypeParamType>());
+      auto substParam = conformanceToWitnessThunkGenericParamFn(param);
+      genericParamTypes.push_back(substParam);
     }
   }
 
diff --git a/lib/AST/SubstitutionMap.cpp b/lib/AST/SubstitutionMap.cpp
index 4e2c64783b8d..663a916bea75 100644
--- a/lib/AST/SubstitutionMap.cpp
+++ b/lib/AST/SubstitutionMap.cpp
@@ -132,9 +132,9 @@ bool SubstitutionMap::hasArchetypes() const {
   return false;
 }
 
-bool SubstitutionMap::hasOpenedExistential() const {
+bool SubstitutionMap::hasLocalArchetypes() const {
   for (Type replacementTy : getReplacementTypesBuffer()) {
-    if (replacementTy && replacementTy->hasOpenedExistential())
+    if (replacementTy && replacementTy->hasLocalArchetype())
       return true;
   }
   return false;
diff --git a/lib/AST/TypeSubstitution.cpp b/lib/AST/TypeSubstitution.cpp
index f0e9d9000a99..c520acd8acee 100644
--- a/lib/AST/TypeSubstitution.cpp
+++ b/lib/AST/TypeSubstitution.cpp
@@ -55,7 +55,13 @@ QueryTypeSubstitutionMapOrIdentity::operator()(SubstitutableType *type) const {
   auto known = substitutions.find(key);
   if (known != substitutions.end() && known->second)
     return known->second;
-  
+
+  if (isa<PackArchetypeType>(type) ||
+      (isa<GenericTypeParamType>(type) &&
+       cast<GenericTypeParamType>(type)->isParameterPack())) {
+    return PackType::getSingletonPackExpansion(type);
+  }
+
   return type;
 }
 
diff --git a/test/SILOptimizer/variadic_generics_sil_cloner.swift b/test/SILOptimizer/variadic_generics_sil_cloner.swift
new file mode 100644
index 000000000000..2ac038a8911f
--- /dev/null
+++ b/test/SILOptimizer/variadic_generics_sil_cloner.swift
@@ -0,0 +1,18 @@
+// RUN: %target-swift-frontend -emit-sil -O %s | %FileCheck %s
+
+@_optimize(none)
+public func callee<T, each X>(_: T, _: repeat each X) {}
+
+@_transparent
+public func caller<each X>(_ x: repeat each X) {
+  repeat callee(each x, repeat each x)
+}
+
+public func outerCaller<each X>(_ x: repeat each X) {
+  caller(repeat each x)
+}
+
+// CHECK-LABEL: sil @$s28variadic_generics_sil_cloner11outerCalleryyxxQpRvzlF : $@convention(thin) <each X> (@pack_guaranteed Pack{repeat each X}) -> () {
+// CHECK: [[CALLEE:%.*]] = function_ref @$s28variadic_generics_sil_cloner6calleeyyx_q_q_QptRv_r0_lF : $@convention(thin) <τ_0_0, each τ_0_1> (@in_guaranteed τ_0_0, @pack_guaranteed Pack{repeat each τ_0_1}) -> ()
+// CHECK: apply [[CALLEE]]<@pack_element("{{.*}}") each X, Pack{repeat each X}>(
+// CHECK: // end sil function '$s28variadic_generics_sil_cloner11outerCalleryyxxQpRvzlF'