diff --git a/modal_proto/api.proto b/modal_proto/api.proto
index 976088a9e3..9babfa35ca 100644
--- a/modal_proto/api.proto
+++ b/modal_proto/api.proto
@@ -2180,6 +2180,7 @@ message RuntimeInputMessage {
   bytes message = 1;
   uint64 message_index = 2;
   bool eof = 3;
+  bool is_resize = 4;
 }
 
 message RuntimeOutputBatch {