diff --git a/hgext/blackbox.py b/hgext/blackbox.py
--- a/hgext/blackbox.py
+++ b/hgext/blackbox.py
@@ -217,6 +217,8 @@ def blackbox(ui, repo, *revs, **opts):
         return
 
     limit = opts.get('limit')
+    assert limit is not None  # help pytype
+
     fp = repo.vfs(b'blackbox.log', b'r')
     lines = fp.read().split(b'\n')
 
diff --git a/hgext/convert/monotone.py b/hgext/convert/monotone.py
--- a/hgext/convert/monotone.py
+++ b/hgext/convert/monotone.py
@@ -243,6 +243,7 @@ class monotone_source(common.converter_s
             m = self.cert_re.match(e)
             if m:
                 name, value = m.groups()
+                assert value is not None  # help pytype
                 value = value.replace(br'\"', b'"')
                 value = value.replace(br'\\', b'\\')
                 certs[name] = value