diff --git a/ctools.install b/ctools.install
index 938ba8504c07e188ecf8e2a87804cc6c82950d96..b52290aa1c6f527efc67c6ffe2ef8f39c1c39cff 100644
--- a/ctools.install
+++ b/ctools.install
@@ -47,6 +47,7 @@ function ctools_schema_2() {
         'type' => 'varchar',
         'length' => '128',
         'description' => t('The CSS ID this cache object belongs to.'),
+        'not null' => TRUE,
       ),
       'filename' => array(
         'type' => 'varchar',