diff --git a/dibs.frontend.inc b/dibs.frontend.inc
index f51cd07..f6f87b3 100644
--- a/dibs.frontend.inc
+++ b/dibs.frontend.inc
@@ -356,7 +356,9 @@ function dibs_frontend_dibs_callback_ok($transaction) {
         $transaction = dibs_transaction_load($transaction['tid']);
 
         // Invoking the module that implemented the payment
-        module_invoke($transaction['api_module'], 'dibsapi', 'transaction_callback', $transaction['api_delta'], $transaction);
+        if (function_exists($function)) {
+          $function('transaction_callback', $transaction['api_delta'], $transaction);
+        }
       }
     }
   }