diff --git a/hgext/phabricator.py b/hgext/phabricator.py
--- a/hgext/phabricator.py
+++ b/hgext/phabricator.py
@@ -161,7 +161,8 @@
     def process(prefix, obj):
         if isinstance(obj, bool):
             obj = {True: b'true', False: b'false'}[obj]  # Python -> PHP form
-        items = {list: enumerate, dict: lambda x: x.items()}.get(type(obj))
+        lister = lambda l: [(b'%d' % k, v) for k, v in enumerate(l)]
+        items = {list: lister, dict: lambda x: x.items()}.get(type(obj))
         if items is None:
             flatparams[prefix] = obj
         else: