diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index a63aa163dd47..898a6bf973c6 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,8 @@
 2011-12-17  Jason Merrill  <jason@redhat.com>
 
+	PR c++/51586
+	* parser.c (cp_parser_check_class_key): Handle error_mark_node.
+
 	PR c++/51587
 	* decl.c (start_enum): Avoid using ENUM_UNDERLYING_TYPE on a
 	non-enum.
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 30c7745caab2..ac7427e5e85c 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -22624,6 +22624,8 @@ cp_parser_token_is_class_key (cp_token* token)
 static void
 cp_parser_check_class_key (enum tag_types class_key, tree type)
 {
+  if (type == error_mark_node)
+    return;
   if ((TREE_CODE (type) == UNION_TYPE) != (class_key == union_type))
     {
       permerror (input_location, "%qs tag used in naming %q#T",
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 71194f56be3c..066121dcd36f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2011-12-17  Jason Merrill  <jason@redhat.com>
 
+	PR c++/51586
+	* g++.dg/lookup/nested2.C: New.
+
 	PR c++/51587
 	* g++.dg/parse/enum6.C: New.
 
diff --git a/gcc/testsuite/g++.dg/lookup/nested2.C b/gcc/testsuite/g++.dg/lookup/nested2.C
new file mode 100644
index 000000000000..361a0c75d566
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/nested2.C
@@ -0,0 +1,6 @@
+// PR c++/51586
+
+union U
+{
+  union U { int i; };		// { dg-error "same name" }
+};