diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 86e7e74793..c46e1318a6 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -358,6 +358,9 @@ create_plan_recurse(PlannerInfo *root, Path *best_path, int flags)
 {
 	Plan	   *plan;
 
+	/* Guard against stack overflow due to overly complex plans */
+	check_stack_depth();
+
 	switch (best_path->pathtype)
 	{
 		case T_SeqScan:
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index e6b15348c1..b586f941a8 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -267,6 +267,9 @@ recurse_set_operations(Node *setOp, PlannerInfo *root,
 					   List **pTargetList,
 					   double *pNumGroups)
 {
+	/* Guard against stack overflow due to overly complex setop nests */
+	check_stack_depth();
+
 	if (IsA(setOp, RangeTblRef))
 	{
 		RangeTblRef *rtr = (RangeTblRef *) setOp;