diff --git a/config.ru b/config.ru
index 80e8a7c..68d508a 100644
--- a/config.ru
+++ b/config.ru
@@ -4,7 +4,7 @@ set :run, false
 set :environment, :production
 
 FileUtils.mkdir_p 'log' unless File.exists?('log')
-log = File.new("log/sinatra.log", "a")
+log = File.new("log/sinatra.log", "a+")
 $stdout.reopen(log)
 $stderr.reopen(log)