diff --git a/packages/oidc/test/mock_client.dart b/packages/oidc/test/mock_client.dart
index d130823..6236f61 100644
--- a/packages/oidc/test/mock_client.dart
+++ b/packages/oidc/test/mock_client.dart
@@ -76,7 +76,7 @@ Future<Response> _handleRequest(
   final url = request.url;
 
   if (_eq.equals(url.pathSegments, ['.well-known', 'openid-configuration'])) {
-    return Response(jsonEncode(mockProviderMetadata), 304);
+    return Response(jsonEncode(mockProviderMetadata), 200);
   }
   if (url.pathSegments.first == 'token') {
     final tokenResp = createMockTokenResponse(
diff --git a/packages/oidc_core/lib/src/endpoints/facade.dart b/packages/oidc_core/lib/src/endpoints/facade.dart
index 62ea43c..05ff049 100644
--- a/packages/oidc_core/lib/src/endpoints/facade.dart
+++ b/packages/oidc_core/lib/src/endpoints/facade.dart
@@ -20,6 +20,7 @@ class OidcEndpoints {
   }) {
     try {
       final body = jsonDecode(response.body) as Map<String, dynamic>;
+
       if (body.containsKey(OidcConstants_AuthParameters.error)) {
         final resp = OidcErrorResponse.fromJson(body);
         throw OidcException.serverError(
@@ -28,6 +29,13 @@ class OidcEndpoints {
           rawResponse: response,
         );
       }
+      if (!(response.statusCode >= 200 && response.statusCode < 400)) {
+        throw OidcException(
+          'Failed to handle the response from endpoint (status code ${response.statusCode}): ${request.url}',
+          rawRequest: request,
+          rawResponse: response,
+        );
+      }
       return mapper(body);
     } on OidcException {
       rethrow;