diff --git a/src/Oro/Bundle/WorkflowBundle/Validator/Constraints/WorkflowEntityValidator.php b/src/Oro/Bundle/WorkflowBundle/Validator/Constraints/WorkflowEntityValidator.php
index ff132699003..a4cc86506fc 100644
--- a/src/Oro/Bundle/WorkflowBundle/Validator/Constraints/WorkflowEntityValidator.php
+++ b/src/Oro/Bundle/WorkflowBundle/Validator/Constraints/WorkflowEntityValidator.php
@@ -198,7 +198,9 @@ protected function validateAllowedValues($object, $message, $restriction)
     {
         $fieldValue = $this->propertyAccessor->getValue($object, $restriction['field']);
         if (is_object($fieldValue)) {
-            $fieldValue = $this->doctrineHelper->getSingleEntityIdentifier($fieldValue);
+            $fieldValue = $this->doctrineHelper->isManageableEntity($fieldValue) ?
+                $this->doctrineHelper->getSingleEntityIdentifier($fieldValue) :
+                (string)$fieldValue;
         }
 
         if ($restriction['mode'] === 'allow') {