diff --git a/lib/kgrader/jail.rb b/lib/kgrader/jail.rb
index 84c841e..1a0cc8d 100644
--- a/lib/kgrader/jail.rb
+++ b/lib/kgrader/jail.rb
@@ -12,7 +12,7 @@ module KGrader
 
     def init
       FileUtils.mkdir_p @root
-      @salt = rand 100000000
+      @salt = rand(100000000).to_s
     end
 
     def stage(source, target)