diff --git a/lib/api/api.rb b/lib/api/api.rb
index 60858a39407..d2a35c78fc1 100644
--- a/lib/api/api.rb
+++ b/lib/api/api.rb
@@ -19,7 +19,7 @@ module API
       message << "  " << trace.join("\n  ")
 
       API.logger.add Logger::FATAL, message
-      rack_response({ 'message' => '500 Internal Server Error' }, 500)
+      rack_response({ 'message' => '500 Internal Server Error' }.to_json, 500)
     end
 
     format :json