Index: testsuite/g++.dg/cpp0x/auto25.C
===================================================================
--- testsuite/g++.dg/cpp0x/auto25.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/auto25.C	(revision 0)
@@ -0,0 +1,7 @@
+// PR c++/42056
+// { dg-options -std=c++0x }
+
+template<int> struct A
+{
+  int a[auto(1)]; // { dg-error "invalid use of" }
+};
Index: testsuite/g++.dg/cpp0x/auto26.C
===================================================================
--- testsuite/g++.dg/cpp0x/auto26.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/auto26.C	(revision 0)
@@ -0,0 +1,7 @@
+// PR c++/42056
+// { dg-options -std=c++0x }
+
+template<int> void foo()
+{
+  int a[auto(1)]; // { dg-error "invalid use of" }
+}
Index: cp/typeck2.c
===================================================================
--- cp/typeck2.c	(revision 174301)
+++ cp/typeck2.c	(working copy)
@@ -1603,6 +1603,14 @@ build_functional_cast (tree exp, tree parms, tsubs
     {
       tree t;
 
+      if (type_uses_auto (type))
+	{
+	  if (complain & tf_error)
+	    error ("invalid use of %<auto%>");
+	  else
+	    return error_mark_node;
+	}
+
       /* Diagnose this even in a template.  We could also try harder
 	 to give all the usual errors when the type and args are
 	 non-dependent...  */