diff --git a/src/mpi/model/null-message-mpi-interface.cc b/src/mpi/model/null-message-mpi-interface.cc
--- a/src/mpi/model/null-message-mpi-interface.cc
+++ b/src/mpi/model/null-message-mpi-interface.cc
@@ -145,8 +145,12 @@
 NullMessageMpiInterface::Enable (int* pargc, char*** pargv)
 {
   NS_LOG_FUNCTION (this << *pargc);
-#ifdef NS3_MPI
 
+#ifndef NS3_MPI
+  NS_UNUSED(pargv);
+  
+#else
+  
   // Initialize the MPI interface
   MPI_Init (pargc, pargv);
   MPI_Barrier (MPI_COMM_WORLD);
diff --git a/src/mpi/model/remote-channel-bundle-manager.cc b/src/mpi/model/remote-channel-bundle-manager.cc
--- a/src/mpi/model/remote-channel-bundle-manager.cc
+++ b/src/mpi/model/remote-channel-bundle-manager.cc
@@ -59,10 +59,10 @@
   return remoteChannelBundle;
 }
 
-uint32_t 
+uint32_t
 RemoteChannelBundleManager::Size (void) 
 {
-  return g_remoteChannelBundles.size();
+  return static_cast<uint32_t> (g_remoteChannelBundles.size());
 }
 
 void
diff --git a/src/mpi/model/remote-channel-bundle.cc b/src/mpi/model/remote-channel-bundle.cc
--- a/src/mpi/model/remote-channel-bundle.cc
+++ b/src/mpi/model/remote-channel-bundle.cc
@@ -40,7 +40,7 @@
 }
 
 RemoteChannelBundle::RemoteChannelBundle ()
-  : m_remoteSystemId (-1),
+  : m_remoteSystemId (UINT32_MAX),
     m_guaranteeTime (0),
     m_delay (NS_TIME_INFINITY)
 {
@@ -98,10 +98,10 @@
   return m_nullEventId;
 }
 
-int
+uint32_t
 RemoteChannelBundle::GetSize (void) const
 {
-  return m_channels.size ();
+  return static_cast<uint32_t> (m_channels.size ());
 }
 
 void 
diff --git a/src/mpi/model/remote-channel-bundle.h b/src/mpi/model/remote-channel-bundle.h
--- a/src/mpi/model/remote-channel-bundle.h
+++ b/src/mpi/model/remote-channel-bundle.h
@@ -98,7 +98,7 @@
   /**
    * \return number of NS3 channels in this bundle
    */
-  int GetSize (void) const;
+  uint32_t GetSize (void) const;
 
   /**
    * \param time