diff --git a/src/wifi/model/wifi-phy.cc b/src/wifi/model/wifi-phy.cc
index e08d100ac..25191fa63 100644
--- a/src/wifi/model/wifi-phy.cc
+++ b/src/wifi/model/wifi-phy.cc
@@ -1764,9 +1764,9 @@ WifiPhy::NotifyMonitorSniffTx (Ptr<const WifiPsdu> psdu, uint16_t channelFreqMhz
           for (size_t i = 0; i < nMpdus;)
             {
               m_phyMonitorSniffTxTrace (psdu->GetAmpduSubframe (i), channelFreqMhz, txVector, aMpdu, staId);
+              ++i;
+              aMpdu.type = (i == (nMpdus - 1)) ? LAST_MPDU_IN_AGGREGATE : MIDDLE_MPDU_IN_AGGREGATE;
             }
-          ++i;
-          aMpdu.type = (i == (nMpdus - 1)) ? LAST_MPDU_IN_AGGREGATE : MIDDLE_MPDU_IN_AGGREGATE;
         }
     }
   else