diff --git a/src/ZfcUser/Authentication/Adapter/Db.php b/src/ZfcUser/Authentication/Adapter/Db.php
index 3b59202a..967d63dc 100644
--- a/src/ZfcUser/Authentication/Adapter/Db.php
+++ b/src/ZfcUser/Authentication/Adapter/Db.php
@@ -75,6 +75,8 @@ public function authenticate(AuthenticationEvent $event)
                 case 'email':
                     $userObject = $this->getMapper()->findByEmail($identity);
                     break;
+                default: 
+                    throw new \InvalidArgumentException('Given an unsupported value');
             }
         }