diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -3341,7 +3341,8 @@
                 )
             # checking that newnodes exist because old state files won't have it
             elif statedata.get(b'newnodes') is not None:
-                nn = statedata[b'newnodes']  # type: List[bytes]
+                nn = statedata[b'newnodes']
+                assert isinstance(nn, list)  # list of bytes
                 nn.append(node)
 
     # remove state when we complete successfully