diff --git a/srtcore/buffer_rcv.h b/srtcore/buffer_rcv.h
index a5e113dfc..4a8e5b078 100644
--- a/srtcore/buffer_rcv.h
+++ b/srtcore/buffer_rcv.h
@@ -325,6 +325,8 @@ class CRcvBufferNew
 
     void setPeerRexmitFlag(bool flag) { m_bPeerRexmitFlag = flag; } 
 
+    void applyGroupISN(int rcv_isn) { m_iStartSeqNo = rcv_isn; }
+
     void applyGroupTime(const time_point& timebase, bool wrp, uint32_t delay, const duration& udrift);
 
     void applyGroupDrift(const time_point& timebase, bool wrp, const duration& udrift);
diff --git a/srtcore/core.cpp b/srtcore/core.cpp
index e9f333d3a..abab5ae6a 100644
--- a/srtcore/core.cpp
+++ b/srtcore/core.cpp
@@ -3330,6 +3330,11 @@ void srt::CUDT::synchronizeWithGroup(CUDTGroup* gp)
                     << " (shift by " << CSeqNo::seqcmp(snd_isn, m_iSndLastAck) << ")");
             setInitialRcvSeq(rcv_isn);
             setInitialSndSeq(snd_isn);
+#if ENABLE_NEW_RCVBUFFER
+            enterCS(m_RecvLock);
+            m_pRcvBuffer->applyGroupISN(rcv_isn);
+            leaveCS(m_RecvLock);
+#endif
         }
         else
         {