diff --git a/src/server/internalServer.cpp b/src/server/internalServer.cpp
index 6f98b4095..a2fa89fe8 100644
--- a/src/server/internalServer.cpp
+++ b/src/server/internalServer.cpp
@@ -888,7 +888,6 @@ std::unique_ptr<Response> InternalServer::handle_search(const RequestContext& re
     return handle_search_request(request);
   } catch (const Error& e) {
     return HTTP400Response(*this, request)
-      + invalidUrlMsg
       + e.message();
   }
 }
diff --git a/src/server/response.cpp b/src/server/response.cpp
index 36a2da244..e3c501798 100644
--- a/src/server/response.cpp
+++ b/src/server/response.cpp
@@ -152,8 +152,6 @@ std::unique_ptr<Response> Response::build_304(const InternalServer& server, cons
   return response;
 }
 
-const InvalidUrlMsg invalidUrlMsg;
-
 std::string ContentResponseBlueprint::getMessage(const std::string& msgId) const
 {
   return getTranslatedString(m_request.get_user_language(), msgId);
@@ -226,17 +224,13 @@ HTTP400Response::HTTP400Response(const InternalServer& server,
                       MHD_HTTP_BAD_REQUEST,
                       "400-page-title",
                       "400-page-heading")
-{
-}
-
-HTTPErrorResponse& HTTP400Response::operator+(InvalidUrlMsg /*unused*/)
 {
   std::string requestUrl = urlDecode(m_request.get_full_url(), false);
   const auto query = m_request.get_query();
   if (!query.empty()) {
     requestUrl += "?" + encodeDiples(query);
   }
-  return *this + ParameterizedMessage("invalid-request", {{"url", requestUrl}});
+  *this += ParameterizedMessage("invalid-request", {{"url", requestUrl}});
 }
 
 HTTP500Response::HTTP500Response(const InternalServer& server,
diff --git a/src/server/response.h b/src/server/response.h
index 46ed4775f..931bfb2f7 100644
--- a/src/server/response.h
+++ b/src/server/response.h
@@ -177,8 +177,6 @@ struct HTTP404Response : HTTPErrorResponse
 {
   HTTP404Response(const InternalServer& server,
                   const RequestContext& request);
-
-  using HTTPErrorResponse::operator+;
 };
 
 struct UrlNotFoundResponse : HTTP404Response
@@ -187,17 +185,10 @@ struct UrlNotFoundResponse : HTTP404Response
                       const RequestContext& request);
 };
 
-class InvalidUrlMsg {};
-
-extern const InvalidUrlMsg invalidUrlMsg;
-
 struct HTTP400Response : HTTPErrorResponse
 {
   HTTP400Response(const InternalServer& server,
                   const RequestContext& request);
-
-  using HTTPErrorResponse::operator+;
-  HTTPErrorResponse& operator+(InvalidUrlMsg /*unused*/);
 };
 
 struct HTTP500Response : HTTPErrorResponse