diff --git a/src/google/protobuf/message.h b/src/google/protobuf/message.h
index 0526e89b85..22ab4c28ae 100644
--- a/src/google/protobuf/message.h
+++ b/src/google/protobuf/message.h
@@ -169,6 +169,7 @@ class MessageReflectionFriend;
 }  // namespace python
 namespace expr {
 class CelMapReflectionFriend;  // field_backed_map_impl.cc
+class SudoMapReflectionFriend;
 }
 
 namespace internal {