diff --git a/osi_streamingupdate.proto b/osi_streamingupdate.proto
index 7445fdca2..78f634090 100644
--- a/osi_streamingupdate.proto
+++ b/osi_streamingupdate.proto
@@ -82,5 +82,7 @@ message StreamingUpdate
     // Entities that will no longer be updated, because they are considered
     // obsolete by the sender.
     //
+    // \note Referenced IDs are globally unique.
+    //
     repeated Identifier obsolete_id = 9;
 }