diff --git a/auto_nodetitle.module b/auto_nodetitle.module
index 30e6e4f..44e6894 100644
--- a/auto_nodetitle.module
+++ b/auto_nodetitle.module
@@ -85,7 +85,7 @@ function auto_nodetitle_set_title(&$node) {
     $node->title = t('@type', array('@type' => $types[$node->type]->name));
   }
   // Ensure the generated title isn't too long.
-  $node->title = substr($node->title, 0, 255);
+  $node->title = drupal_substr($node->title, 0, 255);
   // With that flag we ensure we don't apply the title two times to the same
   // node. See auto_nodetitle_is_needed().
   $node->auto_nodetitle_applied = TRUE;