diff --git a/python/map.c b/python/map.c
index 4330aae..bbbd636 100644
--- a/python/map.c
+++ b/python/map.c
@@ -184,7 +184,7 @@
     map = PyUpb_MapContainer_EnsureReified(_self);
     upb_Arena* arena = PyUpb_Arena_Get(self->arena);
     if (upb_FieldDef_IsSubMessage(val_f)) {
-      const upb_Message* m = upb_FieldDef_MessageSubDef(val_f);
+      const upb_MessageDef* m = upb_FieldDef_MessageSubDef(val_f);
       const upb_MiniTable* layout = upb_MessageDef_MiniTable(m);
       u_val.msg_val = upb_Message_New(layout, arena);
     } else {