diff --git a/module/Rest/src/ErrorHandler/JsonErrorResponseGenerator.php b/module/Rest/src/ErrorHandler/JsonErrorResponseGenerator.php
index 6b865e59..664e693a 100644
--- a/module/Rest/src/ErrorHandler/JsonErrorResponseGenerator.php
+++ b/module/Rest/src/ErrorHandler/JsonErrorResponseGenerator.php
@@ -35,7 +35,7 @@ class JsonErrorResponseGenerator implements ErrorResponseGeneratorInterface, Sta
      * @param string $responsePhrase
      * @return string
      */
-    protected function responsePhraseToCode($responsePhrase)
+    protected function responsePhraseToCode($responsePhrase): string
     {
         return strtoupper(str_replace(' ', '_', $responsePhrase));
     }