diff --git a/Form/DataTransformer/EntitiesToPropertyTransformer.php b/Form/DataTransformer/EntitiesToPropertyTransformer.php
index d6a9fd8..9b33aea 100644
--- a/Form/DataTransformer/EntitiesToPropertyTransformer.php
+++ b/Form/DataTransformer/EntitiesToPropertyTransformer.php
@@ -118,7 +118,7 @@ public function reverseTransform($values)
 
           // this will happen if the form submits invalid data
         if (count($entities) != count($values)) {
-            throw new TransformationFailedException('One or more id values are invalid');
+            throw new TransformationFailedException('One or more ' . $primaryKey . ' values are invalid');
         }
 
         return array_merge($entities, $newObjects);