diff --git a/lib/sinatra/irb.rb b/lib/sinatra/irb.rb
index 76d0473c..6d35af60 100644
--- a/lib/sinatra/irb.rb
+++ b/lib/sinatra/irb.rb
@@ -28,6 +28,7 @@ module Sinatra
             f.puts
             f.puts body
           end
+          nil
         end
         alias :mate :show!