diff --git a/submit.py b/submit.py
index 50be21a..0006a83 100755
--- a/submit.py
+++ b/submit.py
@@ -257,7 +257,7 @@ def submit(submit_url, cookies, problem, language, files, mainclass='', tag=''):
 
     sub_files = []
     for f in files:
-        with open(f) as sub_file:
+        with open(f, 'rb') as sub_file:
             sub_files.append(('sub_file[]',
                               (os.path.basename(f),
                                sub_file.read(),