diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -5569,7 +5569,7 @@
 
 public:
   bool isSugared() const { return true; }
-  QualType desugar() const { return getCanonicalTypeInternal(); }
+  QualType desugar() const;
 
   static bool classof(const Type *T) {
     return T->getTypeClass() == ObjCTypeParam;
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -663,6 +663,10 @@
   initialize(protocols);
 }
 
+QualType ObjCTypeParamType::desugar() const {
+  return getDecl()->getUnderlyingType();
+}
+
 ObjCObjectType::ObjCObjectType(QualType Canonical, QualType Base,
                                ArrayRef<QualType> typeArgs,
                                ArrayRef<ObjCProtocolDecl *> protocols,
diff --git a/clang/test/SemaObjC/parameterized_classes_subst.m b/clang/test/SemaObjC/parameterized_classes_subst.m
--- a/clang/test/SemaObjC/parameterized_classes_subst.m
+++ b/clang/test/SemaObjC/parameterized_classes_subst.m
@@ -467,3 +467,17 @@
 - (void)mapUsingBlock2:(id)block { // expected-warning{{conflicting parameter types in implementation}}
 }
 @end
+
+// --------------------------------------------------------------------------
+// Use a type parameter as a type argument.
+// --------------------------------------------------------------------------
+// Type bounds in a category/extension are omitted. rdar://problem/54329242
+@interface ParameterizedContainer<T : id<NSCopying>>
+- (ParameterizedContainer<T> *)inInterface;
+@end
+@interface ParameterizedContainer<T> (Cat)
+- (ParameterizedContainer<T> *)inCategory;
+@end
+@interface ParameterizedContainer<U> ()
+- (ParameterizedContainer<U> *)inExtension;
+@end