diff --git a/python/servo/command_base.py b/python/servo/command_base.py
index 7184010442cc..9dfa6795d121 100644
--- a/python/servo/command_base.py
+++ b/python/servo/command_base.py
@@ -110,9 +110,9 @@ def reset(tarinfo):
         # packaging (in case of exceptional situations like running out of disk space).
         # TODO do this in a temporary folder after #11983 is fixed
         temp_file = '{}.temp~'.format(dest_archive)
-        with os.fdopen(os.open(temp_file, os.O_WRONLY | os.O_CREAT, 0o644), 'w') as out_file:
+        with os.fdopen(os.open(temp_file, os.O_WRONLY | os.O_CREAT, 0o644), 'wb') as out_file:
             if dest_archive.endswith('.zip'):
-                with zipfile.ZipFile(temp_file, 'w', zipfile.ZIP_DEFLATED) as zip_file:
+                with zipfile.ZipFile(out_file, 'w', zipfile.ZIP_DEFLATED) as zip_file:
                     for entry in file_list:
                         arcname = entry
                         if prepend_path is not None: