diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index f0b053e2f6..615ed1f410 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -6155,13 +6155,19 @@ get_setop_query(Node *setOp, Query *query, deparse_context *context)
 		Query	   *subquery = rte->subquery;
 
 		Assert(subquery != NULL);
-		Assert(subquery->setOperations == NULL);
-		/* Need parens if WITH, ORDER BY, FOR UPDATE, or LIMIT; see gram.y */
+
+		/*
+		 * We need parens if WITH, ORDER BY, FOR UPDATE, or LIMIT; see gram.y.
+		 * Also add parens if the leaf query contains its own set operations.
+		 * (That shouldn't happen unless one of the other clauses is also
+		 * present, see transformSetOperationTree; but let's be safe.)
+		 */
 		need_paren = (subquery->cteList ||
 					  subquery->sortClause ||
 					  subquery->rowMarks ||
 					  subquery->limitOffset ||
-					  subquery->limitCount);
+					  subquery->limitCount ||
+					  subquery->setOperations);
 		if (need_paren)
 			appendStringInfoChar(buf, '(');
 		get_query_def(subquery, buf, context->namespaces,