diff -r 03f7d0822ec1 -r d7d3164e6a31 hgext/phabricator.py
--- a/hgext/phabricator.py	Tue Dec 11 22:34:07 2018 +0900
+++ b/hgext/phabricator.py	Fri Dec 21 17:36:12 2018 -0500
@@ -155,6 +155,8 @@
     """
     flatparams = util.sortdict()
     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))
         if items is None:
             flatparams[prefix] = obj