diff --git a/lib/rscons/cache.rb b/lib/rscons/cache.rb
index ea86386..15fb886 100644
--- a/lib/rscons/cache.rb
+++ b/lib/rscons/cache.rb
@@ -68,7 +68,7 @@ module Rscons
     end
 
     def calculate_checksum(file)
-      Digest::MD5.hexdigest(File.read(file))
+      Digest::MD5.hexdigest(File.read(file)).encode(__ENCODING__)
     end
   end
 end