diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 03674e8990..d14c3c98e1 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.97 2003/06/29 23:05:04 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.98 2003/07/16 17:25:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -85,6 +85,14 @@ plan_set_operations(Query *parse)
 
 	Assert(topop && IsA(topop, SetOperationStmt));
 
+	/* check for unsupported stuff */
+	Assert(parse->utilityStmt == NULL);
+	Assert(parse->jointree->fromlist == NIL);
+	Assert(parse->jointree->quals == NULL);
+	Assert(parse->groupClause == NIL);
+	Assert(parse->havingQual == NULL);
+	Assert(parse->distinctClause == NIL);
+
 	/*
 	 * Find the leftmost component Query.  We need to use its column names
 	 * for all generated tlists (else SELECT INTO won't work right).
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 90818b153b..ca7759cfc8 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.278 2003/07/03 19:07:30 tgl Exp $
+ *	$Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.279 2003/07/16 17:25:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1787,6 +1787,15 @@ transformRuleStmt(ParseState *pstate, RuleStmt *stmt,
 			 */
 			sub_qry = getInsertSelectQuery(top_subqry, NULL);
 
+			/*
+			 * If the sub_qry is a setop, we cannot attach any qualifications
+			 * to it, because the planner won't notice them.  This could
+			 * perhaps be relaxed someday, but for now, we may as well reject
+			 * such a rule immediately.
+			 */
+			if (sub_qry->setOperations != NULL && stmt->whereClause != NULL)
+				elog(ERROR, "Conditional UNION/INTERSECT/EXCEPT statements are not implemented");
+
 			/*
 			 * Validate action's use of OLD/NEW, qual too
 			 */
@@ -1841,6 +1850,13 @@ transformRuleStmt(ParseState *pstate, RuleStmt *stmt,
 			 */
 			if (has_old || (has_new && stmt->event == CMD_UPDATE))
 			{
+				/*
+				 * If sub_qry is a setop, manipulating its jointree will do
+				 * no good at all, because the jointree is dummy.  (This
+				 * should be a can't-happen case because of prior tests.)
+				 */
+				if (sub_qry->setOperations != NULL)
+					elog(ERROR, "Conditional UNION/INTERSECT/EXCEPT statements are not implemented");
 				/* hack so we can use addRTEtoQuery() */
 				sub_pstate->p_rtable = sub_qry->rtable;
 				sub_pstate->p_joinlist = sub_qry->jointree->fromlist;
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index a1d9122f82..7ee28291e0 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.122 2003/07/03 16:34:25 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.123 2003/07/16 17:25:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -148,18 +148,31 @@ rewriteRuleAction(Query *parsetree,
 	 * As above, the action's jointree must not share substructure with the
 	 * main parsetree's.
 	 */
-	if (sub_action->jointree != NULL)
+	if (sub_action->commandType != CMD_UTILITY)
 	{
 		bool		keeporig;
 		List	   *newjointree;
 
+		Assert(sub_action->jointree != NULL);
 		keeporig = (!rangeTableEntry_used((Node *) sub_action->jointree,
 										  rt_index, 0)) &&
 			(rangeTableEntry_used(rule_qual, rt_index, 0) ||
 		  rangeTableEntry_used(parsetree->jointree->quals, rt_index, 0));
 		newjointree = adjustJoinTreeList(parsetree, !keeporig, rt_index);
-		sub_action->jointree->fromlist =
-			nconc(newjointree, sub_action->jointree->fromlist);
+		if (newjointree != NIL)
+		{
+			/*
+			 * If sub_action is a setop, manipulating its jointree will do
+			 * no good at all, because the jointree is dummy.  (Perhaps
+			 * someday we could push the joining and quals down to the
+			 * member statements of the setop?)
+			 */
+			if (sub_action->setOperations != NULL)
+				elog(ERROR, "Conditional UNION/INTERSECT/EXCEPT statements are not implemented");
+
+			sub_action->jointree->fromlist =
+				nconc(newjointree, sub_action->jointree->fromlist);
+		}
 	}
 
 	/*
diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
index 0d3dbe7d6e..1cd42a44f7 100644
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteManip.c,v 1.72 2003/06/06 15:04:02 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteManip.c,v 1.73 2003/07/16 17:25:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -733,6 +733,16 @@ AddQual(Query *parsetree, Node *qual)
 			elog(ERROR, "Conditional utility statements are not implemented");
 	}
 
+	if (parsetree->setOperations != NULL)
+	{
+		/*
+		 * There's noplace to put the qual on a setop statement, either.
+		 * (This could be fixed, but right now the planner simply ignores
+		 * any qual condition on a setop query.)
+		 */
+		elog(ERROR, "Conditional UNION/INTERSECT/EXCEPT statements are not implemented");
+	}
+
 	/* INTERSECT want's the original, but we need to copy - Jan */
 	copy = copyObject(qual);
 
@@ -773,6 +783,16 @@ AddHavingQual(Query *parsetree, Node *havingQual)
 			elog(ERROR, "Conditional utility statements are not implemented");
 	}
 
+	if (parsetree->setOperations != NULL)
+	{
+		/*
+		 * There's noplace to put the qual on a setop statement, either.
+		 * (This could be fixed, but right now the planner simply ignores
+		 * any qual condition on a setop query.)
+		 */
+		elog(ERROR, "Conditional UNION/INTERSECT/EXCEPT statements are not implemented");
+	}
+
 	/* INTERSECT want's the original, but we need to copy - Jan */
 	copy = copyObject(havingQual);