Index: clang/lib/AST/DeclCXX.cpp
===================================================================
--- clang/lib/AST/DeclCXX.cpp
+++ clang/lib/AST/DeclCXX.cpp
@@ -2410,7 +2410,7 @@
     return false;
 
   QualType ParamType = getParamDecl(0)->getType();
-  if (!isa<RValueReferenceType>(ParamType))
+  if (!ParamType->isRValueReferenceType())
     return false;
   ParamType = ParamType->getPointeeType();
 
Index: clang/test/SemaCXX/cxx0x-defaulted-functions.cpp
===================================================================
--- clang/test/SemaCXX/cxx0x-defaulted-functions.cpp
+++ clang/test/SemaCXX/cxx0x-defaulted-functions.cpp
@@ -259,3 +259,28 @@
 
   static_assert(noexcept(A::B()), "");
 }
+
+namespace GH56456 {
+template <typename T>
+using RC=T const&;
+template <typename T>
+using RV=T&;
+template <typename T>
+using RM=T&&;
+
+struct A {
+  A(RC<A>) = default;
+  A(RM<A>) = default;
+
+  auto operator=(RC<A>) -> RV<A> = default;
+  auto operator=(RM<A>) -> RV<A> = default;
+};
+
+struct B {
+  B (RC<B>) = delete;
+  B (RM<B>) = delete;
+
+  auto operator = (RC<B>) -> RV<B> = delete;
+  auto operator = (RM<B>) -> RV<B> = delete;
+};
+}