diff --git a/src/backend/catalog/pg_inherits.c b/src/backend/catalog/pg_inherits.c
index 1bd8a58b7f..74903a8f24 100644
--- a/src/backend/catalog/pg_inherits.c
+++ b/src/backend/catalog/pg_inherits.c
@@ -242,6 +242,40 @@ find_all_inheritors(Oid parentrelId, LOCKMODE lockmode, List **numparents)
 }
 
 
+/*
+ * get_superclasses -
+ *		Returns a list of relation OIDs of direct parents
+ */
+List *
+get_superclasses(Oid relationId)
+{
+	List	   *list = NIL;
+	Relation	catalog;
+	SysScanDesc scan;
+	ScanKeyData skey;
+	HeapTuple	inheritsTuple;
+	Oid			inhparent;
+
+	catalog = heap_open(InheritsRelationId, AccessShareLock);
+	ScanKeyInit(&skey, Anum_pg_inherits_inhrelid, BTEqualStrategyNumber,
+				F_OIDEQ, ObjectIdGetDatum(relationId));
+	scan = systable_beginscan(catalog, InheritsRelidSeqnoIndexId, true,
+							  NULL, 1, &skey);
+
+	while ((inheritsTuple = systable_getnext(scan)) != NULL)
+	{
+		inhparent = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhparent;
+		list = lappend_oid(list, inhparent);
+	}
+
+	systable_endscan(scan);
+
+	heap_close(catalog, AccessShareLock);
+
+	return list;
+}
+
+
 /*
  * has_subclass - does this relation have any children?
  *
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index d979ce266d..c76fc3715d 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -5683,6 +5683,8 @@ ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode)
 	Relation	attr_rel;
 	List	   *indexoidlist;
 	ListCell   *indexoidscan;
+	List	   *parentlist;
+	ListCell   *parentscan;
 	ObjectAddress address;
 
 	/*
@@ -5773,6 +5775,24 @@ ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode)
 		heap_close(parent, AccessShareLock);
 	}
 
+	/* If rel has parents, shoudn't drop NOT NULL if parent has the same */
+	parentlist = get_superclasses(RelationGetRelid(rel));
+	foreach(parentscan, parentlist) {
+		Oid			parentId = lfirst_oid(parentscan);
+		Relation	parent = heap_open(parentId, AccessShareLock);
+		TupleDesc	tupDesc = RelationGetDescr(parent);
+		AttrNumber	parent_attnum;
+
+		parent_attnum = get_attnum(parentId, colName);
+		if (parent_attnum != InvalidAttrNumber &&
+			TupleDescAttr(tupDesc, parent_attnum - 1)->attnotnull)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("column \"%s\" is marked NOT NULL in parent table",
+							colName)));
+		heap_close(parent, AccessShareLock);
+	}
+
 	/*
 	 * Okay, actually perform the catalog change ... if needed
 	 */
diff --git a/src/include/catalog/pg_inherits_fn.h b/src/include/catalog/pg_inherits_fn.h
index 7743388899..291861b846 100644
--- a/src/include/catalog/pg_inherits_fn.h
+++ b/src/include/catalog/pg_inherits_fn.h
@@ -20,6 +20,7 @@
 extern List *find_inheritance_children(Oid parentrelId, LOCKMODE lockmode);
 extern List *find_all_inheritors(Oid parentrelId, LOCKMODE lockmode,
 					List **parents);
+extern List *get_superclasses(Oid relationId);
 extern bool has_subclass(Oid relationId);
 extern bool has_superclass(Oid relationId);
 extern bool typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId);