diff --git a/src/flow-monitor/model/flow-monitor.cc b/src/flow-monitor/model/flow-monitor.cc
index 4814802f2..1223f00d0 100644
--- a/src/flow-monitor/model/flow-monitor.cc
+++ b/src/flow-monitor/model/flow-monitor.cc
@@ -83,6 +83,9 @@ FlowMonitor::FlowMonitor ()
   : m_enabled (false)
 {
   NS_LOG_FUNCTION (this);
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_relaxed);
+#endif
 }
 
 void
@@ -146,6 +149,12 @@ FlowMonitor::ReportFirstTx (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t pack
       return;
     }
   Time now = Simulator::Now ();
+
+#ifdef NS3_MTP
+  while (m_lock.exchange (true, std::memory_order_acquire))
+    ;
+#endif
+
   TrackedPacket &tracked = m_trackedPackets[std::make_pair (flowId, packetId)];
   tracked.firstSeenTime = now;
   tracked.lastSeenTime = tracked.firstSeenTime;
@@ -163,6 +172,10 @@ FlowMonitor::ReportFirstTx (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t pack
       stats.timeFirstTxPacket = now;
     }
   stats.timeLastTxPacket = now;
+
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_release);
+#endif
 }
 
 
@@ -175,6 +188,12 @@ FlowMonitor::ReportForwarding (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t p
       NS_LOG_DEBUG ("FlowMonitor not enabled; returning");
       return;
     }
+
+#ifdef NS3_MTP
+  while (m_lock.exchange (true, std::memory_order_acquire))
+    ;
+#endif
+
   std::pair<FlowId, FlowPacketId> key (flowId, packetId);
   TrackedPacketMap::iterator tracked = m_trackedPackets.find (key);
   if (tracked == m_trackedPackets.end ())
@@ -189,6 +208,10 @@ FlowMonitor::ReportForwarding (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t p
 
   Time delay = (Simulator::Now () - tracked->second.firstSeenTime);
   probe->AddPacketStats (flowId, packetSize, delay);
+
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_release);
+#endif
 }
 
 
@@ -201,6 +224,12 @@ FlowMonitor::ReportLastRx (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t packe
       NS_LOG_DEBUG ("FlowMonitor not enabled; returning");
       return;
     }
+
+#ifdef NS3_MTP
+  while (m_lock.exchange (true, std::memory_order_acquire))
+    ;
+#endif
+
   TrackedPacketMap::iterator tracked = m_trackedPackets.find (std::make_pair (flowId, packetId));
   if (tracked == m_trackedPackets.end ())
     {
@@ -255,6 +284,10 @@ FlowMonitor::ReportLastRx (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t packe
                 << flowId << ", packetId=" << packetId << ").");
 
   m_trackedPackets.erase (tracked); // we don't need to track this packet anymore
+
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_release);
+#endif
 }
 
 void
@@ -268,6 +301,11 @@ FlowMonitor::ReportDrop (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t packetI
       return;
     }
 
+#ifdef NS3_MTP
+  while (m_lock.exchange (true, std::memory_order_acquire))
+    ;
+#endif
+
   probe->AddPacketDropStats (flowId, packetSize, reasonCode);
 
   FlowStats &stats = GetStatsForFlow (flowId);
@@ -290,6 +328,10 @@ FlowMonitor::ReportDrop (Ptr<FlowProbe> probe, uint32_t flowId, uint32_t packetI
                     << flowId << ", packetId=" << packetId << ").");
       m_trackedPackets.erase (tracked);
     }
+
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_release);
+#endif
 }
 
 const FlowMonitor::FlowStatsContainer&
diff --git a/src/flow-monitor/model/flow-monitor.h b/src/flow-monitor/model/flow-monitor.h
index d0c1d481c..3352bedd6 100644
--- a/src/flow-monitor/model/flow-monitor.h
+++ b/src/flow-monitor/model/flow-monitor.h
@@ -23,6 +23,7 @@
 
 #include <vector>
 #include <map>
+#include <atomic>
 
 #include "ns3/ptr.h"
 #include "ns3/object.h"
@@ -294,6 +295,9 @@ private:
   double m_packetSizeBinWidth;  //!< packet size bin width (for histograms)
   double m_flowInterruptionsBinWidth; //!< Flow interruptions bin width (for histograms)
   Time m_flowInterruptionsMinTime; //!< Flow interruptions minimum time
+#ifdef NS3_MTP
+  std::atomic<bool> m_lock;
+#endif
 
   /// Get the stats for a given flow
   /// \param flowId the Flow identification
diff --git a/src/flow-monitor/model/ipv4-flow-classifier.cc b/src/flow-monitor/model/ipv4-flow-classifier.cc
index 6a103f9ee..67b8192d6 100644
--- a/src/flow-monitor/model/ipv4-flow-classifier.cc
+++ b/src/flow-monitor/model/ipv4-flow-classifier.cc
@@ -98,6 +98,9 @@ bool operator == (const Ipv4FlowClassifier::FiveTuple &t1,
 
 Ipv4FlowClassifier::Ipv4FlowClassifier ()
 {
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_relaxed);
+#endif
 }
 
 bool
@@ -147,6 +150,11 @@ Ipv4FlowClassifier::Classify (const Ipv4Header &ipHeader, Ptr<const Packet> ipPa
   tuple.sourcePort = srcPort;
   tuple.destinationPort = dstPort;
 
+#ifdef NS3_MTP
+  while (m_lock.exchange (true, std::memory_order_acquire))
+    ;
+#endif
+
   // try to insert the tuple, but check if it already exists
   std::pair<std::map<FiveTuple, FlowId>::iterator, bool> insert
     = m_flowMap.insert (std::pair<FiveTuple, FlowId> (tuple, 0));
@@ -178,6 +186,10 @@ Ipv4FlowClassifier::Classify (const Ipv4Header &ipHeader, Ptr<const Packet> ipPa
   *out_flowId = insert.first->second;
   *out_packetId = m_flowPktIdMap[*out_flowId];
 
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_release);
+#endif
+
   return true;
 }
 
diff --git a/src/flow-monitor/model/ipv4-flow-classifier.h b/src/flow-monitor/model/ipv4-flow-classifier.h
index dbc64198e..05418e8f8 100644
--- a/src/flow-monitor/model/ipv4-flow-classifier.h
+++ b/src/flow-monitor/model/ipv4-flow-classifier.h
@@ -23,6 +23,7 @@
 
 #include <stdint.h>
 #include <map>
+#include <atomic>
 
 #include "ns3/ipv4-header.h"
 #include "ns3/flow-classifier.h"
@@ -99,6 +100,9 @@ private:
   /// Map FlowIds to (DSCP value, packet count) pairs
   std::map<FlowId, std::map<Ipv4Header::DscpType, uint32_t> > m_flowDscpMap;
 
+#ifdef NS3_MTP
+  std::atomic<bool> m_lock;
+#endif
 };
 
 /**
diff --git a/src/flow-monitor/model/ipv6-flow-classifier.cc b/src/flow-monitor/model/ipv6-flow-classifier.cc
index 85ce1f4ea..5db15a4dd 100644
--- a/src/flow-monitor/model/ipv6-flow-classifier.cc
+++ b/src/flow-monitor/model/ipv6-flow-classifier.cc
@@ -99,6 +99,9 @@ bool operator == (const Ipv6FlowClassifier::FiveTuple &t1,
 
 Ipv6FlowClassifier::Ipv6FlowClassifier ()
 {
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_relaxed);
+#endif
 }
 
 bool
@@ -148,6 +151,11 @@ Ipv6FlowClassifier::Classify (const Ipv6Header &ipHeader, Ptr<const Packet> ipPa
   tuple.sourcePort = srcPort;
   tuple.destinationPort = dstPort;
 
+#ifdef NS3_MTP
+  while (m_lock.exchange (true, std::memory_order_acquire))
+    ;
+#endif
+
   // try to insert the tuple, but check if it already exists
   std::pair<std::map<FiveTuple, FlowId>::iterator, bool> insert
     = m_flowMap.insert (std::pair<FiveTuple, FlowId> (tuple, 0));
@@ -179,6 +187,10 @@ Ipv6FlowClassifier::Classify (const Ipv6Header &ipHeader, Ptr<const Packet> ipPa
   *out_flowId = insert.first->second;
   *out_packetId = m_flowPktIdMap[*out_flowId];
 
+#ifdef NS3_MTP
+  m_lock.store (false, std::memory_order_release);
+#endif
+
   return true;
 }
 
diff --git a/src/flow-monitor/model/ipv6-flow-classifier.h b/src/flow-monitor/model/ipv6-flow-classifier.h
index d6b2aacc9..45f978cb5 100644
--- a/src/flow-monitor/model/ipv6-flow-classifier.h
+++ b/src/flow-monitor/model/ipv6-flow-classifier.h
@@ -24,6 +24,7 @@
 
 #include <stdint.h>
 #include <map>
+#include <atomic>
 
 #include "ns3/ipv6-header.h"
 #include "ns3/flow-classifier.h"
@@ -100,6 +101,9 @@ private:
   /// Map FlowIds to (DSCP value, packet count) pairs
   std::map<FlowId, std::map<Ipv6Header::DscpType, uint32_t> > m_flowDscpMap;
 
+#ifdef NS3_MTP
+  std::atomic<bool> m_lock;
+#endif
 };
 
 /**