Index: sql_table.cc
===================================================================
--- sql_table.cc	(revision 21155)
+++ sql_table.cc	(working copy)
@@ -7229,7 +7229,7 @@
                                     alter_info->keys_onoff,
                                     alter_info->error_if_not_empty);
   }
-  else
+  else if (alter_info->flags & ALTER_KEYS_ONOFF)
   {
     VOID(pthread_mutex_lock(&LOCK_open));
     wait_while_table_is_used(thd, table, HA_EXTRA_FORCE_REOPEN);