diff --git a/sqlsrv/schema.inc b/sqlsrv/schema.inc
index c38a7e4..01fc8ac 100755
--- a/sqlsrv/schema.inc
+++ b/sqlsrv/schema.inc
@@ -171,7 +171,7 @@ class DatabaseSchema_sqlsrv extends DatabaseSchema {
         $sql .= ' IDENTITY';
       }
       if (!empty($spec['unsigned'])) {
-        $sql .= ' CHECK (' . $name . ' >= 0)';
+        $sql .= ' CHECK ([' . $name . '] >= 0)';
       }
     }
     return $sql;