diff --git a/extensions/nicknames/src/AddNicknameValidation.php b/extensions/nicknames/src/AddNicknameValidation.php
index 2f9b27418f..5ce43e840d 100644
--- a/extensions/nicknames/src/AddNicknameValidation.php
+++ b/extensions/nicknames/src/AddNicknameValidation.php
@@ -40,7 +40,7 @@ public function __invoke($flarumValidator, Validator $validator)
             function ($attribute, $value, $fail) {
                 $regex = $this->settings->get('flarum-nicknames.regex');
                 if ($regex && ! preg_match_all("/$regex/", $value)) {
-                    $this->translator->trans('flarum-nicknames.api.invalid_nickname_message');
+                    $fail($this->translator->trans('flarum-nicknames.api.invalid_nickname_message'));
                 }
             },
             'min:'.$this->settings->get('flarum-nicknames.min'),
diff --git a/extensions/nicknames/tests/integration/api/RegisterTest.php b/extensions/nicknames/tests/integration/api/RegisterTest.php
index e1ae8e0407..af050ab3fc 100644
--- a/extensions/nicknames/tests/integration/api/RegisterTest.php
+++ b/extensions/nicknames/tests/integration/api/RegisterTest.php
@@ -74,4 +74,48 @@ public function cant_register_with_nickname_if_not_allowed()
 
         $this->assertEquals(403, $response->getStatusCode());
     }
+
+    /**
+     * @test
+     */
+    public function cant_register_with_nickname_if_invalid_regex()
+    {
+        $this->setting('flarum-nicknames.set_on_registration', true);
+        $this->setting('flarum-nicknames.regex', '^[A-z]+$');
+
+        $response = $this->send(
+            $this->request('POST', '/register', [
+                'json' => [
+                    'nickname' => '007',
+                    'username' => 'test',
+                    'password' => 'too-obscure',
+                    'email' => 'test@machine.local',
+                ]
+            ])
+        );
+
+        $this->assertEquals(422, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function can_register_with_nickname_if_valid_regex()
+    {
+        $this->setting('flarum-nicknames.set_on_registration', true);
+        $this->setting('flarum-nicknames.regex', '^[A-z]+$');
+
+        $response = $this->send(
+            $this->request('POST', '/register', [
+                'json' => [
+                    'nickname' => 'Acme',
+                    'username' => 'test',
+                    'password' => 'too-obscure',
+                    'email' => 'test@machine.local',
+                ]
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+    }
 }