diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1839,9 +1839,18 @@
 
     QualType Replacement = Arg.getAsType();
 
-    // TODO: only do this uniquing once, at the start of instantiation.
-    QualType Result
-      = getSema().Context.getSubstTemplateTypeParmType(T, Replacement);
+    QualType Result;
+    if (T->isParameterPack()) {
+      QualType NewT = getSema().Context.getTemplateTypeParmType(
+          T->getDepth(),
+          T->getIndex() + getSema().ArgumentPackSubstitutionIndex, false);
+      Result = getSema().Context.getSubstTemplateTypeParmType(
+          cast<TemplateTypeParmType>(NewT), Replacement);
+    } else {
+      // TODO: only do this uniquing once, at the start of instantiation.
+      Result = getSema().Context.getSubstTemplateTypeParmType(T, Replacement);
+    }
+
     SubstTemplateTypeParmTypeLoc NewTL
       = TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
     NewTL.setNameLoc(TL.getNameLoc());
@@ -1879,11 +1888,14 @@
 
   TemplateArgument Arg = TL.getTypePtr()->getArgumentPack();
   Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
-  QualType Result = Arg.getAsType();
 
-  Result = getSema().Context.getSubstTemplateTypeParmType(
-                                      TL.getTypePtr()->getReplacedParameter(),
-                                                          Result);
+  const TemplateTypeParmType *T = TL.getTypePtr()->getReplacedParameter();
+  QualType NewT = getSema().Context.getTemplateTypeParmType(
+      T->getDepth(), T->getIndex() + getSema().ArgumentPackSubstitutionIndex,
+      false);
+  QualType Result = getSema().Context.getSubstTemplateTypeParmType(
+      cast<TemplateTypeParmType>(NewT), Arg.getAsType());
+
   SubstTemplateTypeParmTypeLoc NewTL
     = TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
   NewTL.setNameLoc(TL.getNameLoc());
diff --git a/clang/test/AST/ast-dump-template-decls.cpp b/clang/test/AST/ast-dump-template-decls.cpp
--- a/clang/test/AST/ast-dump-template-decls.cpp
+++ b/clang/test/AST/ast-dump-template-decls.cpp
@@ -137,13 +137,13 @@
 using t1 = foo<int, short>::bind<char, float>;
 // CHECK:      TemplateSpecializationType 0x{{[^ ]*}} 'Y<char, float, int, short>' sugar Y
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'char' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'Bs' dependent contains_unexpanded_pack depth 0 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-0' dependent depth 0 index 0
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'float' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'Bs' dependent contains_unexpanded_pack depth 0 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-1' dependent depth 0 index 1
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'Bs' dependent contains_unexpanded_pack depth 0 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-2' dependent depth 0 index 2
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'short' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'Bs' dependent contains_unexpanded_pack depth 0 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-3' dependent depth 0 index 3
 
 template <typename... T> struct D {
   template <typename... U> using B = int(int (*...p)(T, U));
@@ -153,12 +153,12 @@
 // CHECK:      FunctionProtoType 0x{{[^ ]*}} 'int (int (*)(float, int), int (*)(char, short))' cdecl
 // CHECK:      FunctionProtoType 0x{{[^ ]*}} 'int (float, int)' cdecl
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'float' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'T' dependent contains_unexpanded_pack depth 0 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-0' dependent depth 0 index 0
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'U' dependent contains_unexpanded_pack depth 1 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-1-0' dependent depth 1 index 0
 // CHECK:      FunctionProtoType 0x{{[^ ]*}} 'int (char, short)' cdecl
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'char' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'T' dependent contains_unexpanded_pack depth 0 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-1' dependent depth 0 index 1
 // CHECK:      SubstTemplateTypeParmType 0x{{[^ ]*}} 'short' sugar
-// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'U' dependent contains_unexpanded_pack depth 1 index 0 pack
+// CHECK-NEXT: TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-1-1' dependent depth 1 index 1
 } // namespace PR56099