diff --git a/src/osmformat.proto b/src/osmformat.proto
index 6373349..73f6472 100644
--- a/src/osmformat.proto
+++ b/src/osmformat.proto
@@ -78,7 +78,7 @@ message PrimitiveBlock {
 
 
   // Proposed extension:
-  //optional BBox bbox = 19;
+  //optional BBox bbox = XX;
 }
 
 // Group of OSMPrimitives. All primitives in a group must be the same type.