Index: testsuite/g++.dg/parse/template26.C
===================================================================
--- testsuite/g++.dg/parse/template26.C	(revision 0)
+++ testsuite/g++.dg/parse/template26.C	(revision 0)
@@ -0,0 +1,18 @@
+// PR c++/50864
+
+namespace impl
+{
+  template <class T> T create();
+}
+
+template <class T, class U, __SIZE_TYPE__
+	  = sizeof(impl::create<T>()->*impl::create<U>())>
+struct foo1;
+
+template <class T, class U, __SIZE_TYPE__
+	  = sizeof(impl::create<T>()->impl::create<U>())> // { dg-error "not a class member" }
+struct foo2;
+
+template <class T, class U, __SIZE_TYPE__
+	  = sizeof(impl::create<T>().impl::create<U>())> // { dg-error "not a class member" }
+struct foo3;
Index: cp/parser.c
===================================================================
--- cp/parser.c	(revision 181133)
+++ cp/parser.c	(working copy)
@@ -5969,10 +5969,19 @@ cp_parser_postfix_dot_deref_expression (cp_parser
 	{
 	  if (name != error_mark_node && !BASELINK_P (name) && parser->scope)
 	    {
-	      name = build_qualified_name (/*type=*/NULL_TREE,
-					   parser->scope,
-					   name,
-					   template_p);
+	      if (TREE_CODE (parser->scope) == NAMESPACE_DECL
+		  && (TREE_CODE (postfix_expression) == ARROW_EXPR
+		      || TREE_CODE (postfix_expression) == CALL_EXPR))
+		{
+		  error_at (token->location, "%<%D::%D%> is not a class member",
+			    parser->scope, name);
+		  postfix_expression = error_mark_node;
+		}
+	      else
+		name = build_qualified_name (/*type=*/NULL_TREE,
+					     parser->scope,
+					     name,
+					     template_p);
 	      parser->scope = NULL_TREE;
 	      parser->qualifying_scope = NULL_TREE;
 	      parser->object_scope = NULL_TREE;