diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 60e663c9cc8..95134bfeda3 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -4950,8 +4950,8 @@ var_is_nonnullable(PlannerInfo *root, Var *var, NotNullSource source)
 				 * Note that we need to check if the relation actually has any
 				 * children, as we might not have done that yet.
 				 */
-				if (rte->inh && has_subclass(rte->relid) &&
-					rte->relkind != RELKIND_PARTITIONED_TABLE)
+				if (rte->relkind != RELKIND_PARTITIONED_TABLE &&
+					rte->inh && has_subclass(rte->relid))
 					return false;
 
 				/* We need not lock the relation since it was already locked */
@@ -5100,14 +5100,6 @@ expr_is_nonnullable(PlannerInfo *root, Expr *expr, NotNullSource source)
 				 */
 				return true;
 			}
-		case T_DistinctExpr:
-			{
-				/*
-				 * IS DISTINCT FROM never returns NULL, effectively acting as
-				 * though NULL were a normal data value.
-				 */
-				return true;
-			}
 		case T_RelabelType:
 			{
 				/*
diff --git a/src/test/regress/expected/predicate.out b/src/test/regress/expected/predicate.out
index feae77cb840..22fe4308af3 100644
--- a/src/test/regress/expected/predicate.out
+++ b/src/test/regress/expected/predicate.out
@@ -611,16 +611,6 @@ SELECT * FROM pred_tab WHERE ((a > 1) IS TRUE) IS NULL;
    One-Time Filter: false
 (3 rows)
 
--- DistinctExpr
-EXPLAIN (COSTS OFF)
-SELECT * FROM pred_tab WHERE (a IS DISTINCT FROM b) IS NULL;
-          QUERY PLAN          
-------------------------------
- Result
-   Replaces: Scan on pred_tab
-   One-Time Filter: false
-(3 rows)
-
 -- RelabelType
 EXPLAIN (COSTS OFF)
 SELECT * FROM pred_tab WHERE (a::oid) IS NULL;
diff --git a/src/test/regress/sql/predicate.sql b/src/test/regress/sql/predicate.sql
index 0f92bb52435..9dd236efb56 100644
--- a/src/test/regress/sql/predicate.sql
+++ b/src/test/regress/sql/predicate.sql
@@ -299,10 +299,6 @@ SELECT * FROM pred_tab WHERE (b IS NULL) IS NULL;
 EXPLAIN (COSTS OFF)
 SELECT * FROM pred_tab WHERE ((a > 1) IS TRUE) IS NULL;
 
--- DistinctExpr
-EXPLAIN (COSTS OFF)
-SELECT * FROM pred_tab WHERE (a IS DISTINCT FROM b) IS NULL;
-
 -- RelabelType
 EXPLAIN (COSTS OFF)
 SELECT * FROM pred_tab WHERE (a::oid) IS NULL;