diff --git a/rietveld.py b/rietveld.py
index dc8404f08..7397b295b 100644
--- a/rietveld.py
+++ b/rietveld.py
@@ -257,7 +257,7 @@ class Rietveld(object):
     return self.post('/%d/edit_flags' % issue, [
         ('last_patchset', str(patchset)),
         ('xsrf_token', self.xsrf_token()),
-        (flag, value)])
+        (flag, str(value))])
 
   def search(
       self,