diff --git a/RELEASE_NOTES b/RELEASE_NOTES
index c829e0320..715d2f102 100644
--- a/RELEASE_NOTES
+++ b/RELEASE_NOTES
@@ -26,6 +26,7 @@ Bugs fixed
 ----------
 - Bug 2007 - uan: Remove deprecation on SetRxThresholdDb
 - Bug 2450 - LogDistancePropagationLossModel is not continuous
+- Bug 2477 - DCF manager assert
 - Bug 2492 - uan: Make use of RxGain attribute in UanPhyGen class
 - Bug 2511 - HT Greenfield is not working
 - Bug 2521 - Include ipv6-option.h in wscript
diff --git a/src/wifi/model/dcf-manager.cc b/src/wifi/model/dcf-manager.cc
index 2b08323dc..f1ace9335 100644
--- a/src/wifi/model/dcf-manager.cc
+++ b/src/wifi/model/dcf-manager.cc
@@ -808,27 +808,13 @@ DcfManager::NotifyTxStartNow (Time duration)
   NS_LOG_FUNCTION (this << duration);
   if (m_rxing)
     {
-      if (Simulator::Now () - m_lastRxStart <= m_sifs)
-        {
-          //this may be caused if PHY has started to receive a packet
-          //inside SIFS, so, we check that lastRxStart was within a SIFS ago
-          m_lastRxEnd = Simulator::Now ();
-          m_lastRxDuration = m_lastRxEnd - m_lastRxStart;
-          m_lastRxReceivedOk = true;
-          m_rxing = false;
-        }
-      else
-        {
-          // Bug 2477:  It is possible for the DCF to fall out of 
-          //            sync with the PHY state if there are problems
-          //            receiving A-MPDUs.  PHY will cancel the reception
-          //            and start to transmit
-          NS_LOG_DEBUG ("Phy is transmitting despite DCF being in receive state");
-          m_lastRxEnd = Simulator::Now ();
-          m_lastRxDuration = m_lastRxEnd - m_lastRxStart;
-          m_lastRxReceivedOk = false;
-          m_rxing = false;
-        }
+      //this may be caused only if PHY has started to receive a packet
+      //inside SIFS, so, we check that lastRxStart was maximum a SIFS ago
+      NS_ASSERT (Simulator::Now () - m_lastRxStart <= m_sifs);
+      m_lastRxEnd = Simulator::Now ();
+      m_lastRxDuration = m_lastRxEnd - m_lastRxStart;
+      m_lastRxReceivedOk = true;
+      m_rxing = false;
     }
   MY_DEBUG ("tx start for " << duration);
   UpdateBackoff ();
diff --git a/src/wifi/model/mac-low.cc b/src/wifi/model/mac-low.cc
index ad8cb5b88..42496c1b7 100644
--- a/src/wifi/model/mac-low.cc
+++ b/src/wifi/model/mac-low.cc
@@ -845,7 +845,7 @@ void
 MacLow::ReceiveError (Ptr<Packet> packet, double rxSnr)
 {
   NS_LOG_FUNCTION (this << packet << rxSnr);
-  NS_LOG_DEBUG ("rx failed ");
+  NS_LOG_DEBUG ("rx failed");
   if (m_txParams.MustWaitFastAck ())
     {
       NS_ASSERT (m_fastAckFailedTimeoutEvent.IsExpired ());
@@ -1681,9 +1681,9 @@ MacLow::ForwardDown (Ptr<const Packet> packet, const WifiMacHeader* hdr,
           
           if (delay == Seconds (0))
             {
+              NS_LOG_DEBUG ("Sending MPDU as part of A-MPDU");
               if (!vhtSingleMpdu)
                 {
-                  NS_LOG_DEBUG ("Sending MPDU as part of A-MPDU");
                   mpdutype = MPDU_IN_AGGREGATE;
                 }
               else
@@ -2698,23 +2698,30 @@ MacLow::SendBlockAckResponse (const CtrlBAckResponseHeader* blockAck, Mac48Addre
 void
 MacLow::SendBlockAckAfterAmpdu (uint8_t tid, Mac48Address originator, Time duration, WifiTxVector blockAckReqTxVector, double rxSnr)
 {
-  NS_LOG_FUNCTION (this << (uint16_t) tid << originator << duration.As (Time::S) << blockAckReqTxVector << rxSnr);
-  CtrlBAckResponseHeader blockAck;
-  uint16_t seqNumber = 0;
-  BlockAckCachesI i = m_bAckCaches.find (std::make_pair (originator, tid));
-  NS_ASSERT (i != m_bAckCaches.end ());
-  seqNumber = (*i).second.GetWinStart ();
+  if (!m_phy->IsStateTx () && !m_phy->IsStateRx ())
+    {
+      NS_LOG_FUNCTION (this << (uint16_t) tid << originator << duration.As (Time::S) << blockAckReqTxVector << rxSnr);
+      CtrlBAckResponseHeader blockAck;
+      uint16_t seqNumber = 0;
+      BlockAckCachesI i = m_bAckCaches.find (std::make_pair (originator, tid));
+      NS_ASSERT (i != m_bAckCaches.end ());
+      seqNumber = (*i).second.GetWinStart ();
 
-  bool immediate = true;
-  AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
-  blockAck.SetStartingSequence (seqNumber);
-  blockAck.SetTidInfo (tid);
-  immediate = (*it).second.first.IsImmediateBlockAck ();
-  blockAck.SetType (COMPRESSED_BLOCK_ACK);
-  NS_LOG_DEBUG ("Got Implicit block Ack Req with seq " << seqNumber);
-  (*i).second.FillBlockAckBitmap (&blockAck);
+      bool immediate = true;
+      AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
+      blockAck.SetStartingSequence (seqNumber);
+      blockAck.SetTidInfo (tid);
+      immediate = (*it).second.first.IsImmediateBlockAck ();
+      blockAck.SetType (COMPRESSED_BLOCK_ACK);
+      NS_LOG_DEBUG ("Got Implicit block Ack Req with seq " << seqNumber);
+      (*i).second.FillBlockAckBitmap (&blockAck);
 
-  SendBlockAckResponse (&blockAck, originator, immediate, duration, blockAckReqTxVector.GetMode (), rxSnr);
+      SendBlockAckResponse (&blockAck, originator, immediate, duration, blockAckReqTxVector.GetMode (), rxSnr);
+    }
+  else
+    {
+      NS_LOG_DEBUG ("Skip block ack response!");
+    }
 }
 
 void