diff --git a/features/steps/mongrel_helper.rb b/features/steps/mongrel_helper.rb
index 8f6105f..99713a5 100644
--- a/features/steps/mongrel_helper.rb
+++ b/features/steps/mongrel_helper.rb
@@ -10,7 +10,7 @@ class BasicMongrelHandler < Mongrel::HttpHandler
   end
 
   def process(request, response)
-    instance_eval &preprocessor if preprocessor
+    instance_eval(&preprocessor) if preprocessor
     reply_with(response, response_code, response_body)
   end