diff --git a/includes/database/mysql/schema.inc b/includes/database/mysql/schema.inc
index 9ba1c73..8e2021f 100644
--- a/includes/database/mysql/schema.inc
+++ b/includes/database/mysql/schema.inc
@@ -337,7 +337,7 @@ class DatabaseSchema_mysql extends DatabaseSchema {
     }
 
     $fixnull = FALSE;
-    if (!empty($spec['not null']) && !isset($spec['default'])) {
+    if ($spec['type'] != 'serial' && !empty($spec['not null']) && !isset($spec['default'])) {
       $fixnull = TRUE;
       $spec['not null'] = FALSE;
     }