Index: lib/Sema/SemaCXXScopeSpec.cpp
===================================================================
--- lib/Sema/SemaCXXScopeSpec.cpp
+++ lib/Sema/SemaCXXScopeSpec.cpp
@@ -846,6 +846,8 @@
   assert(DS.getTypeSpecType() == DeclSpec::TST_decltype);
 
   QualType T = BuildDecltypeType(DS.getRepAsExpr(), DS.getTypeSpecTypeLoc());
+  if (T.getTypePtrOrNull() == nullptr)
+      return true;
   if (!T->isDependentType() && !T->getAs<TagType>()) {
     Diag(DS.getTypeSpecTypeLoc(), diag::err_expected_class_or_namespace) 
       << T << getLangOpts().CPlusPlus;
Index: test/SemaCXX/qualtype-null-check.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/qualtype-null-check.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++14 -verify %s
+struct A
+{
+    bool x{&decltype(foo)::foo}; // expected-error {{reference to non-static member function must be called}}
+    void foo(int);
+};