diff --git a/proto/binaryblob.proto b/proto/binaryblob.proto
index ceb7735..e4b9b8b 100644
--- a/proto/binaryblob.proto
+++ b/proto/binaryblob.proto
@@ -11,5 +11,6 @@
 message BinaryBlobBase {
     optional string blob_base_id = 1; // Common parent path of contained blobs
     repeated BinaryBlob blobs = 2;
-    optional uint32 max_size_bytes = 3;
+    reserved "max_size_bytes";
+    reserved 3;
 }