diff --git a/conditional_fields.module b/conditional_fields.module
index 58a8374..3fe8724 100644
--- a/conditional_fields.module
+++ b/conditional_fields.module
@@ -578,7 +578,9 @@ function conditional_fields_form_after_build($form, &$form_state) {
     // Execute custom behaviors callbacks.
     if (!empty($behaviors)) {
       foreach ($behaviors as $behavior) {
-        $behavior($form, $form_state, $dependent, $dependent_info);
+	if (function_exists($behavior)) {
+          $behavior($form, $form_state, $dependent, $dependent_info);
+        }
       }      
     }