diff --git a/RELEASE_NOTES b/RELEASE_NOTES
index cfc8ce4e4..c492fc9b3 100644
--- a/RELEASE_NOTES
+++ b/RELEASE_NOTES
@@ -67,6 +67,7 @@ Bugs fixed
 - Bug 2414 - UdpSocket doesn't call NotifyConnectionFailed
 - Bug 2419 - BsmApplication should use RecvFrom and not SocketAddressTag
 - Bug 2420 - Remove code duplication between Wifi and Wave modules
+- Bug 2421 - Negative RemainingAmpduDuration for the last MPDU in A-MPDU tag
 - Bug 2425 - UdpSocketImpl simplification
 - Bug 2427 - 802.11ac selects wrong slot duration
 - Bug 2433 - Bic does not copy private parameters
diff --git a/src/wifi/model/mac-low.cc b/src/wifi/model/mac-low.cc
index f3e43cfef..3a8575d7e 100644
--- a/src/wifi/model/mac-low.cc
+++ b/src/wifi/model/mac-low.cc
@@ -1694,7 +1694,14 @@ MacLow::ForwardDown (Ptr<const Packet> packet, const WifiMacHeader* hdr,
           remainingAmpduDuration -= mpduDuration;
 
           ampdutag.SetRemainingNbOfMpdus (queueSize - 1);
-          ampdutag.SetRemainingAmpduDuration (remainingAmpduDuration);
+          if (queueSize > 1)
+            {
+              ampdutag.SetRemainingAmpduDuration (remainingAmpduDuration);
+            }
+          else
+            {
+              ampdutag.SetRemainingAmpduDuration (NanoSeconds (0));
+            }
           newPacket->AddPacketTag (ampdutag);
 
           if (delay == Seconds (0))
@@ -1707,6 +1714,7 @@ MacLow::ForwardDown (Ptr<const Packet> packet, const WifiMacHeader* hdr,
             }
           if (queueSize > 1)
             {
+              NS_ASSERT (remainingAmpduDuration > 0);
               delay = delay + mpduDuration;
             }