diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 7d9c769..f69631f 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -3397,6 +3397,30 @@ AlterTableGetLockLevel(List *cmds)
 }
 
 /*
+ * Some AT commands require to take a lock on the parent prior to the target.
+ */
+void
+AlterTableLockInhParent(List *cmds, LOCKMODE lockmode)
+{
+	ListCell   *lcmd;
+
+	foreach(lcmd, cmds)
+	{
+		AlterTableCmd *cmd = (AlterTableCmd *) lfirst(lcmd);
+
+		switch (cmd->subtype)
+		{		
+		case AT_DropInherit:
+			RangeVarGetRelid((RangeVar *)cmd->def, lockmode, false);
+			break;
+
+		default:
+			break;
+		}
+	}
+}
+
+/*
  * ATController provides top level control over the phases.
  *
  * parsetree is passed in to allow it to be passed to event triggers
@@ -11446,12 +11470,8 @@ ATExecDropInherit(Relation rel, RangeVar *parent, LOCKMODE lockmode)
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("cannot change inheritance of a partition")));
 
-	/*
-	 * AccessShareLock on the parent is probably enough, seeing that DROP
-	 * TABLE doesn't lock parent tables at all.  We need some lock since we'll
-	 * be inspecting the parent's schema.
-	 */
-	parent_rel = heap_openrv(parent, AccessShareLock);
+	/* Requreid lock is already held */
+	parent_rel = heap_openrv(parent, NoLock);
 
 	/*
 	 * We don't bother to check ownership of the parent table --- ownership of
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index ddacac8..ce3406b 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -1102,6 +1102,9 @@ ProcessUtilitySlow(ParseState *pstate,
 					 * permissions.
 					 */
 					lockmode = AlterTableGetLockLevel(atstmt->cmds);
+
+					/* Lock the parent first if required */
+					AlterTableLockInhParent(atstmt->cmds, lockmode);
 					relid = AlterTableLookupRelation(atstmt, lockmode);
 
 					if (OidIsValid(relid))
diff --git a/src/include/commands/tablecmds.h b/src/include/commands/tablecmds.h
index abd31b6..c643326 100644
--- a/src/include/commands/tablecmds.h
+++ b/src/include/commands/tablecmds.h
@@ -27,6 +27,7 @@ extern ObjectAddress DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 
 extern void RemoveRelations(DropStmt *drop);
 
+void AlterTableLockInhParent(List *cmds, LOCKMODE lockmode);
 extern Oid	AlterTableLookupRelation(AlterTableStmt *stmt, LOCKMODE lockmode);
 
 extern void AlterTable(Oid relid, LOCKMODE lockmode, AlterTableStmt *stmt);