diff --git a/build.py b/build.py
index cf2c740..bfd0a95 100644
--- a/build.py
+++ b/build.py
@@ -66,7 +66,7 @@
 
 
 def write_file(zip, path, date):
-    file = path.open()
+    file = path.open('rb')
     data = file.read()
     file.close()
     name = path.as_posix()