diff --git a/src/backend/rewrite/rewriteDefine.c b/src/backend/rewrite/rewriteDefine.c
index 03c5c5ae38..b1f8c6e3ff 100644
--- a/src/backend/rewrite/rewriteDefine.c
+++ b/src/backend/rewrite/rewriteDefine.c
@@ -8,13 +8,14 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteDefine.c,v 1.136 2009/01/27 12:40:15 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteDefine.c,v 1.137 2009/05/13 22:32:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
 #include "access/heapam.h"
+#include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
@@ -242,6 +243,22 @@ DefineQueryRewrite(char *rulename,
 	 */
 	event_relation = heap_open(event_relid, AccessExclusiveLock);
 
+	/*
+	 * Verify relation is of a type that rules can sensibly be applied to.
+	 */
+	if (event_relation->rd_rel->relkind != RELKIND_RELATION &&
+		event_relation->rd_rel->relkind != RELKIND_VIEW)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not a table or view",
+						RelationGetRelationName(event_relation))));
+
+	if (!allowSystemTableMods && IsSystemRelation(event_relation))
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied: \"%s\" is a system catalog",
+						RelationGetRelationName(event_relation))));
+
 	/*
 	 * Check user has permission to apply rules to this relation.
 	 */