diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index f701954..d9f4776 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1473,6 +1473,15 @@ query_is_distinct_for(Query *query, List *colnos, List *opids)
 	Assert(list_length(colnos) == list_length(opids));
 
 	/*
+	 * The presence of set returning functions in the query's target list can
+	 * cause multiple rows per group to exist, so we'll need to play it safe
+	 * here and report that the query is not distinct when set returning
+	 * functions exist.
+	 */
+	if (expression_returns_set((Node *) query->targetList))
+		return false;
+
+	/*
 	 * DISTINCT (including DISTINCT ON) guarantees uniqueness if all the
 	 * columns in the DISTINCT clause appear in colnos and operator semantics
 	 * match.