diff --git a/ox/api.py b/ox/api.py
index b784788..894e26d 100644
--- a/ox/api.py
+++ b/ox/api.py
@@ -100,7 +100,7 @@ class API(object):
             if self.DEBUG:
                 import webbrowser
                 if e.code >= 500:
-                    with open('/tmp/error.html', 'w') as f:
+                    with open('/tmp/error.html', 'wb') as f:
                         f.write(e.read())
                     webbrowser.open_new_tab('/tmp/error.html')