diff --git a/db/blip_handler.go b/db/blip_handler.go
index 67dcd00219..379a5926f9 100644
--- a/db/blip_handler.go
+++ b/db/blip_handler.go
@@ -1084,9 +1084,6 @@ func (bh *blipHandler) processRev(rq *blip.Message, stats *processRevStats) (err
 	if deltaSrcRevID, isDelta := revMessage.DeltaSrc(); isDelta && !revMessage.Deleted() {
 		if !bh.sgCanUseDeltas {
 			return base.HTTPErrorf(http.StatusBadRequest, "Deltas are disabled for this peer")
-		} else if !bh.useHLV() {
-			// Disable delta sync for protocol versions < 4, CBG-3748 (backwards compatibility for revID delta sync)
-			return base.HTTPErrorf(http.StatusBadRequest, "backwards compatibility for revTree deltas not yet implemented")
 		}
 
 		//  TODO: Doing a GetRevCopy here duplicates some rev cache retrieval effort, since deltaRevSrc is always
diff --git a/db/blip_sync_context.go b/db/blip_sync_context.go
index 9fd8eab56a..c16165773c 100644
--- a/db/blip_sync_context.go
+++ b/db/blip_sync_context.go
@@ -355,16 +355,17 @@ func (bsc *BlipSyncContext) handleChangesResponse(ctx context.Context, sender *b
 			}
 
 			// The first element of the knownRevsArray returned from CBL is the parent revision to use as deltaSrc for
-			// revtree clients, for HLV clients the first element is the HLV
+			// revtree clients. For HLV clients, use the cv as deltaSrc
 			if bsc.useDeltas && len(knownRevsArray) > 0 {
 				if revID, ok := knownRevsArray[0].(string); ok {
 					if bsc.useHLV() {
 						msgHLV, err := extractHLVFromBlipMessage(revID)
 						if err != nil {
-							base.ErrorfCtx(ctx, "Invalid known rev format for hlv on doc: %s", docID)
-							return nil
+							base.DebugfCtx(ctx, base.KeySync, "Invalid known rev format for hlv on doc: %s falling back to full body replication.", docID)
+							deltaSrcRevID = "" // will force falling back to full body replication below
+						} else {
+							deltaSrcRevID = msgHLV.GetCurrentVersionString()
 						}
-						deltaSrcRevID = msgHLV.GetCurrentVersionString()
 					} else {
 						deltaSrcRevID = revID
 					}
@@ -373,6 +374,13 @@ func (bsc *BlipSyncContext) handleChangesResponse(ctx context.Context, sender *b
 
 			for _, rev := range knownRevsArray {
 				if revID, ok := rev.(string); ok {
+					msgHLV, err := extractHLVFromBlipMessage(revID)
+					if err == nil {
+						// extract cv as string
+						revID = msgHLV.GetCurrentVersionString()
+					}
+					// we can assume here that if we fail to parse hlv, we have received a rev id in known revs. If we don't fail to parse hlv
+					// then we have extracted cv from it and can assign the cv string to known revs here
 					knownRevs[revID] = true
 				} else {
 					base.ErrorfCtx(ctx, "Invalid response to 'changes' message")
diff --git a/db/revision_cache_interface.go b/db/revision_cache_interface.go
index c43f952c04..46bf3679a9 100644
--- a/db/revision_cache_interface.go
+++ b/db/revision_cache_interface.go
@@ -453,6 +453,7 @@ func revCacheLoaderForDocumentCV(ctx context.Context, backingStore RevisionCache
 		base.ErrorfCtx(ctx, "pending CBG-3814 support of channel removal for CV: %v", err)
 	}
 
+	deleted = doc.Deleted
 	channels = doc.SyncData.getCurrentChannels()
 	revid = doc.CurrentRev
 	hlv = doc.HLV
@@ -462,7 +463,7 @@ func revCacheLoaderForDocumentCV(ctx context.Context, backingStore RevisionCache
 
 func (c *DatabaseCollection) getCurrentVersion(ctx context.Context, doc *Document, cv Version) (bodyBytes []byte, attachments AttachmentsMeta, err error) {
 	if err = doc.HasCurrentVersion(ctx, cv); err != nil {
-		bodyBytes, err = c.getOldRevisionJSON(ctx, doc.ID, doc.CurrentRev)
+		bodyBytes, err = c.getOldRevisionJSON(ctx, doc.ID, cv.String())
 		if err != nil || bodyBytes == nil {
 			return nil, nil, err
 		}