diff --git a/api/models/ChangeUsernameForm.php b/api/models/ChangeUsernameForm.php
index 4333a07..b17095d 100644
--- a/api/models/ChangeUsernameForm.php
+++ b/api/models/ChangeUsernameForm.php
@@ -21,7 +21,7 @@ class ChangeUsernameForm extends PasswordProtectedForm {
         $account = new Account();
         $account->username = $this->$attribute;
         if (!$account->validate(['username'])) {
-            $account->addErrors($account->getErrors('username'));
+            $this->addErrors($account->getErrors());
         }
     }
 
diff --git a/tests/codeception/api/functional/AccountsChangeUsernameCest.php b/tests/codeception/api/functional/AccountsChangeUsernameCest.php
index e0b7805..bdc83f7 100644
--- a/tests/codeception/api/functional/AccountsChangeUsernameCest.php
+++ b/tests/codeception/api/functional/AccountsChangeUsernameCest.php
@@ -28,7 +28,7 @@ class AccountsChangeUsernameCest {
     }
 
     public function testChangeUsername(FunctionalTester $I, Scenario $scenario) {
-        $I->wantTo('change my password');
+        $I->wantTo('change my nickname');
         $I = new AccountSteps($scenario);
         $I->loggedInAsActiveAccount();
 
@@ -40,4 +40,20 @@ class AccountsChangeUsernameCest {
         ]);
     }
 
+    public function testChangeUsernameNotAvailable(FunctionalTester $I, Scenario $scenario) {
+        $I->wantTo('see, that nickname "in use" is not available');
+        $I = new AccountSteps($scenario);
+        $I->loggedInAsActiveAccount();
+
+        $this->route->changeUsername('password_0', 'Jon');
+        $I->canSeeResponseCodeIs(200);
+        $I->canSeeResponseIsJson();
+        $I->canSeeResponseContainsJson([
+            'success' => false,
+            'errors' => [
+                'username' => 'error.username_not_available',
+            ],
+        ]);
+    }
+
 }