diff --git a/indexer/indexer.go b/indexer/indexer.go
index e3c28ec1..66663de0 100644
--- a/indexer/indexer.go
+++ b/indexer/indexer.go
@@ -104,13 +104,20 @@ func (ix *Indexer) HandleRepoEvent(ctx context.Context, evt *repomgr.RepoEvent)
 		toobig = true
 	}
 
+	// Normalize empty string to nil for since field
+	// Empty string fails TID validation on consumers
+	var since *string
+	if evt.Since != nil && *evt.Since != "" {
+		since = evt.Since
+	}
+
 	ix.log.Debug("Sending event", "did", did)
 	if err := ix.events.AddEvent(ctx, &events.XRPCStreamEvent{
 		RepoCommit: &comatproto.SyncSubscribeRepos_Commit{
 			Repo:   did,
 			Blocks: slice,
 			Rev:    evt.Rev,
-			Since:  evt.Since,
+			Since:  since,
 			Commit: lexutil.LexLink(evt.NewRoot),
 			Time:   time.Now().Format(util.ISO8601),
 			Ops:    outops,