1 files changed, 2 insertions, 3 deletions
diff --git a/actionpack/lib/action_dispatch/testing/assertions/response.rb b/actionpack/lib/action_dispatch/testing/assertions/response.rb
index 98b1965d22..8595ea03cf 100644
--- a/actionpack/lib/action_dispatch/testing/assertions/response.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions/response.rb
@@ -79,9 +79,8 @@ module ActionDispatch
         end
 
         def generate_response_message(expected, actual = @response.response_code)
-          "Expected response to be a <#{code_with_name(expected)}>,"\
-          " but was a <#{code_with_name(actual)}>"
-            .dup.concat(location_if_redirected).concat(response_body_if_short)
+          (+"Expected response to be a <#{code_with_name(expected)}>,"\
+          " but was a <#{code_with_name(actual)}>").concat(location_if_redirected).concat(response_body_if_short)
         end
 
         def response_body_if_short