diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 9fb266d089d..cd4e2e86c6d 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -4635,6 +4635,14 @@ var_is_nonnullable(PlannerInfo *root, Var *var, NotNullSource source)
 	if (!bms_is_empty(var->varnullingrels))
 		return false;
 
+	/*
+	 * If the Var has a non-default returning type, it could be NULL
+	 * regardless of any NOT NULL constraint.  For example, OLD.col is NULL
+	 * for INSERT, and NEW.col is NULL for DELETE.
+	 */
+	if (var->varreturningtype != VAR_RETURNING_DEFAULT)
+		return false;
+
 	/* system columns cannot be NULL */
 	if (var->varattno < 0)
 		return true;
diff --git a/src/test/regress/expected/returning.out b/src/test/regress/expected/returning.out
index cfaaf015bb3..196829e94fa 100644
--- a/src/test/regress/expected/returning.out
+++ b/src/test/regress/expected/returning.out
@@ -990,3 +990,34 @@ BEGIN ATOMIC
            WHERE (foo_1.* = n.*)) AS count;
 END
 DROP FUNCTION foo_update;
+-- Test that the planner does not fold OLD/NEW IS NULL tests to constants
+-- based on NOT NULL constraints, since OLD is NULL for INSERT and NEW is
+-- NULL for DELETE.
+CREATE TEMP TABLE ret_nn (a int NOT NULL);
+-- INSERT has no OLD row, should return true
+INSERT INTO ret_nn VALUES (1) RETURNING old.a IS NULL;
+ ?column? 
+----------
+ t
+(1 row)
+
+-- DELETE has no NEW row, should return true
+DELETE FROM ret_nn WHERE a = 1 RETURNING new.a IS NULL;
+ ?column? 
+----------
+ t
+(1 row)
+
+-- MERGE: DELETE should have new.a IS NULL, INSERT should have old.a IS NULL
+INSERT INTO ret_nn VALUES (2);
+MERGE INTO ret_nn USING (VALUES (2), (3)) AS src(a) ON ret_nn.a = src.a
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED THEN INSERT VALUES (src.a)
+  RETURNING merge_action(), old.a IS NULL, new.a IS NULL;
+ merge_action | ?column? | ?column? 
+--------------+----------+----------
+ DELETE       | f        | t
+ INSERT       | t        | f
+(2 rows)
+
+DROP TABLE ret_nn;
diff --git a/src/test/regress/sql/returning.sql b/src/test/regress/sql/returning.sql
index cc99cb53f63..b3c8c5df550 100644
--- a/src/test/regress/sql/returning.sql
+++ b/src/test/regress/sql/returning.sql
@@ -408,3 +408,23 @@ END;
 
 \sf foo_update
 DROP FUNCTION foo_update;
+
+-- Test that the planner does not fold OLD/NEW IS NULL tests to constants
+-- based on NOT NULL constraints, since OLD is NULL for INSERT and NEW is
+-- NULL for DELETE.
+CREATE TEMP TABLE ret_nn (a int NOT NULL);
+
+-- INSERT has no OLD row, should return true
+INSERT INTO ret_nn VALUES (1) RETURNING old.a IS NULL;
+
+-- DELETE has no NEW row, should return true
+DELETE FROM ret_nn WHERE a = 1 RETURNING new.a IS NULL;
+
+-- MERGE: DELETE should have new.a IS NULL, INSERT should have old.a IS NULL
+INSERT INTO ret_nn VALUES (2);
+MERGE INTO ret_nn USING (VALUES (2), (3)) AS src(a) ON ret_nn.a = src.a
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED THEN INSERT VALUES (src.a)
+  RETURNING merge_action(), old.a IS NULL, new.a IS NULL;
+
+DROP TABLE ret_nn;