diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index cd4e2e86c6d..fcf6d7fff2a 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -20,6 +20,7 @@
 #include "postgres.h"
 
 #include "access/htup_details.h"
+#include "access/table.h"
 #include "catalog/pg_class.h"
 #include "catalog/pg_inherits.h"
 #include "catalog/pg_language.h"
@@ -59,6 +60,7 @@
 #include "utils/jsonpath.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/rel.h"
 #include "utils/syscache.h"
 #include "utils/typcache.h"
 
@@ -2134,7 +2136,7 @@ query_outputs_are_not_nullable(Query *query)
 		 * parse tree, we need to look up the not-null constraints from the
 		 * system catalogs.
 		 */
-		if (expr_is_nonnullable(&subroot, expr, NOTNULL_SOURCE_SYSCACHE))
+		if (expr_is_nonnullable(&subroot, expr, NOTNULL_SOURCE_CATALOG))
 			continue;
 
 		if (IsA(expr, Var))
@@ -4696,13 +4698,19 @@ var_is_nonnullable(PlannerInfo *root, Var *var, NotNullSource source)
 
 				return bms_is_member(var->varattno, notnullattnums);
 			}
-		case NOTNULL_SOURCE_SYSCACHE:
+		case NOTNULL_SOURCE_CATALOG:
 			{
 				/*
-				 * We look up the "attnotnull" field in the attribute
-				 * relation.
+				 * We check the attnullability field in the tuple descriptor.
+				 * This is necessary rather than checking the attnotnull field
+				 * from the attribute relation, because attnotnull is also set
+				 * for invalid (NOT VALID) NOT NULL constraints, which do not
+				 * guarantee the absence of NULLs.
 				 */
 				RangeTblEntry *rte;
+				Relation	rel;
+				CompactAttribute *attr;
+				bool		result;
 
 				rte = planner_rt_fetch(var->varno, root);
 
@@ -4723,7 +4731,14 @@ var_is_nonnullable(PlannerInfo *root, Var *var, NotNullSource source)
 					rte->relkind != RELKIND_PARTITIONED_TABLE)
 					return false;
 
-				return get_attnotnull(rte->relid, var->varattno);
+				/* We need not lock the relation since it was already locked */
+				rel = table_open(rte->relid, NoLock);
+				attr = TupleDescCompactAttr(RelationGetDescr(rel),
+											var->varattno - 1);
+				result = (attr->attnullability == ATTNULLABLE_VALID);
+				table_close(rel, NoLock);
+
+				return result;
 			}
 		default:
 			elog(ERROR, "unrecognized NotNullSource: %d",
@@ -4746,9 +4761,9 @@ var_is_nonnullable(PlannerInfo *root, Var *var, NotNullSource source)
  *	- NOTNULL_SOURCE_HASHTABLE: Used when RelOptInfos are not yet available,
  *	but we have already collected relation-level not-null constraints into the
  *	global hash table.
- *	- NOTNULL_SOURCE_SYSCACHE: Used for raw parse trees where neither
- *	RelOptInfos nor the hash table are available.  In this case, we have to
- *	look up the 'attnotnull' field directly in the system catalogs.
+ *	- NOTNULL_SOURCE_CATALOG: Used for raw parse trees where neither
+ *	RelOptInfos nor the hash table are available.  In this case, we check the
+ *	column's attnullability in the tuple descriptor.
  *
  * For now, we support only a limited set of expression types.  Support for
  * additional node types can be added in the future.
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 9b2b97f5cba..fa9fe9ffa26 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -1114,33 +1114,6 @@ get_attoptions(Oid relid, int16 attnum)
 	return result;
 }
 
-/*
- * get_attnotnull
- *
- *		Given the relation id and the attribute number,
- *		return the "attnotnull" field from the attribute relation.
- */
-bool
-get_attnotnull(Oid relid, AttrNumber attnum)
-{
-	HeapTuple	tp;
-	bool		result = false;
-
-	tp = SearchSysCache2(ATTNUM,
-						 ObjectIdGetDatum(relid),
-						 Int16GetDatum(attnum));
-
-	if (HeapTupleIsValid(tp))
-	{
-		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
-
-		result = att_tup->attnotnull;
-		ReleaseSysCache(tp);
-	}
-
-	return result;
-}
-
 /*				---------- PG_CAST CACHE ----------					 */
 
 /*
diff --git a/src/include/optimizer/optimizer.h b/src/include/optimizer/optimizer.h
index e8b409afb7f..cb6241e2bdd 100644
--- a/src/include/optimizer/optimizer.h
+++ b/src/include/optimizer/optimizer.h
@@ -135,7 +135,7 @@ typedef enum
 {
 	NOTNULL_SOURCE_RELOPT,		/* Use RelOptInfo */
 	NOTNULL_SOURCE_HASHTABLE,	/* Use Global Hash Table */
-	NOTNULL_SOURCE_SYSCACHE,	/* Use System Catalog */
+	NOTNULL_SOURCE_CATALOG,		/* Use System Catalog */
 } NotNullSource;
 
 extern bool contain_mutable_functions(Node *clause);
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index e57795fa01f..2e0258d877e 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -99,7 +99,6 @@ extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 								  Oid *typid, int32 *typmod, Oid *collid);
 extern Datum get_attoptions(Oid relid, int16 attnum);
-extern bool get_attnotnull(Oid relid, AttrNumber attnum);
 extern Oid	get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok);
 extern char *get_collation_name(Oid colloid);
 extern bool get_collation_isdeterministic(Oid colloid);
diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index 200236a0a69..a3778c23c34 100644
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -3761,4 +3761,27 @@ WHERE NOT id ?= ANY (SELECT id FROM not_null_tab);
            ->  Seq Scan on not_null_tab not_null_tab_1
 (5 rows)
 
+-- No ANTI JOIN: the inner side has an unvalidated NOT NULL constraint, so
+-- the column might contain NULLs.
+CREATE TEMP TABLE notnull_notvalid_tab (id int);
+INSERT INTO notnull_notvalid_tab VALUES (NULL);
+ALTER TABLE notnull_notvalid_tab ADD CONSTRAINT nn NOT NULL id NOT VALID;
+EXPLAIN (COSTS OFF)
+SELECT * FROM not_null_tab
+WHERE id NOT IN (SELECT id FROM notnull_notvalid_tab);
+                        QUERY PLAN                        
+----------------------------------------------------------
+ Seq Scan on not_null_tab
+   Filter: (NOT (ANY (id = (hashed SubPlan any_1).col1)))
+   SubPlan any_1
+     ->  Seq Scan on notnull_notvalid_tab
+(4 rows)
+
+-- NOT IN with NULL on inner side should return no rows
+SELECT * FROM not_null_tab
+WHERE id NOT IN (SELECT id FROM notnull_notvalid_tab);
+ id | val 
+----+-----
+(0 rows)
+
 ROLLBACK;
diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index 4cd016f4ac3..1a02c3f86c0 100644
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -1632,4 +1632,18 @@ EXPLAIN (COSTS OFF)
 SELECT * FROM not_null_tab
 WHERE NOT id ?= ANY (SELECT id FROM not_null_tab);
 
+-- No ANTI JOIN: the inner side has an unvalidated NOT NULL constraint, so
+-- the column might contain NULLs.
+CREATE TEMP TABLE notnull_notvalid_tab (id int);
+INSERT INTO notnull_notvalid_tab VALUES (NULL);
+ALTER TABLE notnull_notvalid_tab ADD CONSTRAINT nn NOT NULL id NOT VALID;
+
+EXPLAIN (COSTS OFF)
+SELECT * FROM not_null_tab
+WHERE id NOT IN (SELECT id FROM notnull_notvalid_tab);
+
+-- NOT IN with NULL on inner side should return no rows
+SELECT * FROM not_null_tab
+WHERE id NOT IN (SELECT id FROM notnull_notvalid_tab);
+
 ROLLBACK;