diff --git a/AmpTools/IUAmpTools/NormIntInterface.cc b/AmpTools/IUAmpTools/NormIntInterface.cc
index 8e5f53f7..f4fd296b 100644
--- a/AmpTools/IUAmpTools/NormIntInterface.cc
+++ b/AmpTools/IUAmpTools/NormIntInterface.cc
@@ -137,7 +137,7 @@ NormIntInterface::~NormIntInterface(){
 istream&
 NormIntInterface::loadNormIntCache( istream& input )
 {
-  input >> m_nGenEvents >> m_sumAccWeights;
+  input >> m_sumGenWeights >> m_sumAccWeights;
   
   int numTerms;
   input >> numTerms;
@@ -191,7 +191,7 @@ NormIntInterface::operator+=( const NormIntInterface& nii )
   double nGenEvts = nii.numGenEvents();
   
   double totalAccEvts = nAccEvts + m_sumAccWeights;
-  double totalGenEvts = nGenEvts + m_nGenEvents;
+  double totalGenEvts = nGenEvts + m_sumGenWeights;
   
   string ampName, conjAmpName;
   
@@ -212,8 +212,8 @@ NormIntInterface::operator+=( const NormIntInterface& nii )
       m_ampIntCache[2*i*n+j+1] /= totalAccEvts;
 
       
-      m_ampIntCache[2*i*n+j]   *= m_nGenEvents;
-      m_ampIntCache[2*i*n+j+1] *= m_nGenEvents;
+      m_ampIntCache[2*i*n+j]   *= m_sumGenWeights;
+      m_ampIntCache[2*i*n+j+1] *= m_sumGenWeights;
       
       complex< double > ni = nii.normInt( m_termNames[i], m_termNames[j]  );
       
@@ -228,7 +228,7 @@ NormIntInterface::operator+=( const NormIntInterface& nii )
   
   
   m_sumAccWeights = totalAccEvts;
-  m_nGenEvents = totalGenEvts;
+  m_sumGenWeights = totalGenEvts;
   
   m_emptyNormIntCache = false;
   m_emptyAmpIntCache = false;
@@ -280,7 +280,7 @@ NormIntInterface::normInt( string amp, string conjAmp, bool forceUseCache ) cons
     report( DEBUG, kModule ) << "Request for normInt ( " << amp << ", " << conjAmp
     << " ) asking IntensityManager to calculate integrals." << endl;
     
-    m_pIntenManager->calcIntegrals( m_accMCVecs, m_nGenEvents );
+    m_pIntenManager->calcIntegrals( m_accMCVecs, m_sumGenWeights );
     setNormIntMatrix( m_accMCVecs.m_pdIntegralMatrix );
   }
 #endif
@@ -373,7 +373,7 @@ NormIntInterface::forceCacheUpdate( bool normIntOnly ) const
     report( DEBUG, kModule ) << "Asking IntensityManager to update integrals "
                              << "using the accepted MC." << endl;
     
-    m_pIntenManager->calcIntegrals( m_accMCVecs, m_nGenEvents );
+    m_pIntenManager->calcIntegrals( m_accMCVecs, m_sumGenWeights );
     setNormIntMatrix( m_accMCVecs.m_pdIntegralMatrix );
     
     m_emptyNormIntCache = false;
@@ -402,7 +402,7 @@ NormIntInterface::forceCacheUpdate( bool normIntOnly ) const
     report( DEBUG, kModule ) << "Asking IntensityManager to calculate integrals "
     << "using the generated MC." << endl;
     
-    m_pIntenManager->calcIntegrals( m_genMCVecs, m_nGenEvents, m_chunkSize );
+    m_pIntenManager->calcIntegrals( m_genMCVecs, m_sumGenWeights, m_chunkSize );
     
     setAmpIntMatrix( m_genMCVecs.m_pdIntegralMatrix );
 
@@ -427,7 +427,7 @@ NormIntInterface::forceCacheUpdate( bool normIntOnly ) const
   }
   else {
     
-    m_pIntenManager->calcIntegrals( m_accMCVecs, m_nGenEvents );
+    m_pIntenManager->calcIntegrals( m_accMCVecs, m_sumGenWeights );
     setNormIntMatrix( m_accMCVecs.m_pdIntegralMatrix );
   }
   m_emptyNormIntCache = false;
@@ -451,7 +451,11 @@ NormIntInterface::exportNormIntCache( ostream& out ) const
   if( m_emptyNormIntCache || m_emptyAmpIntCache ) forceCacheUpdate();
 #endif
   
-  out << m_nGenEvents << "\t" << m_sumAccWeights << endl;
+  // the static cast produces an output file that is backwards compatible
+  // with older versions that used integer number of generated events
+  // rather than the sum of the weights -- this should not make any
+  // signficant difference in a result
+  out << static_cast<long int>(m_sumGenWeights) << "\t" << m_sumAccWeights << endl;
   
   out << m_termNames.size() << endl;
   
@@ -596,7 +600,7 @@ NormIntInterface::loadMC() const {
     
     genVecs->second->shareDataWith( &m_genMCVecs, m_pIntenManager->needsUserVarsOnly() );
   }
-  m_nGenEvents = m_genMCVecs.m_iNTrueEvents;
+  m_sumGenWeights = m_genMCVecs.m_dSumWeights;
 }
 
 void
diff --git a/AmpTools/IUAmpTools/NormIntInterface.h b/AmpTools/IUAmpTools/NormIntInterface.h
index 07e028d0..67f38dfc 100644
--- a/AmpTools/IUAmpTools/NormIntInterface.h
+++ b/AmpTools/IUAmpTools/NormIntInterface.h
@@ -69,7 +69,7 @@ class NormIntInterface
   istream& loadNormIntCache( istream& in );
   void operator+=( const NormIntInterface& nii );
   
-  size_t numGenEvents() const { return m_nGenEvents; }
+  double numGenEvents() const { return m_sumGenWeights; }
   double numAccEvents() const { return m_sumAccWeights; }
   
   // this integral folds in detector acceptance
@@ -103,7 +103,7 @@ class NormIntInterface
   const double* ampIntMatrix() const  { return m_ampIntCache;  }
   const double* normIntMatrix() const { return m_normIntCache; }
   
-  void setGenEvents( size_t events ) { m_nGenEvents = events; }
+  void setGenEvents( double sumWeights ) { m_sumGenWeights = sumWeights; }
   void setAccEvents( double sumWeights ) { m_sumAccWeights = sumWeights; }
   
 protected:
@@ -135,7 +135,7 @@ class NormIntInterface
   mutable bool m_emptyNormIntCache;
   mutable bool m_emptyAmpIntCache;
   
-  mutable size_t m_nGenEvents;
+  mutable double m_sumGenWeights;
   mutable double m_sumAccWeights;
   
 #ifndef __ACLIC__
diff --git a/AmpTools/IUAmpToolsMPI/NormIntInterfaceMPI.cc b/AmpTools/IUAmpToolsMPI/NormIntInterfaceMPI.cc
index 70a9b911..0a5e675e 100644
--- a/AmpTools/IUAmpToolsMPI/NormIntInterfaceMPI.cc
+++ b/AmpTools/IUAmpToolsMPI/NormIntInterfaceMPI.cc
@@ -95,35 +95,34 @@ NormIntInterfaceMPI::setupMPI()
   
   m_isLeader = ( m_rank == 0 );
   
-  long int totalGenEvents = 0;
+  double totalGenWeights = 0;
   double totalAccWeights = 0;
     
   if( m_isLeader ){
     
     for( int i = 1; i < m_numProc; ++i ){
       
-      size_t thisEvents;
       double thisWeights;
 
       // trigger sending of events from followers -- data is irrelevant
-      MPI_Send( &thisEvents, 1, MPI_LONG, i, MPITag::kAcknowledge,
+      MPI_Send( &thisWeights, 1, MPI_DOUBLE, i, MPITag::kAcknowledge,
                MPI_COMM_WORLD );
       
       // now receive actual data
-      MPI_Recv( &thisEvents, 1, MPI_LONG, i, MPITag::kIntSend,
+      MPI_Recv( &thisWeights, 1, MPI_DOUBLE, i, MPITag::kDoubleSend,
                MPI_COMM_WORLD, &status );
-      totalGenEvents += thisEvents;
+      totalGenWeights += thisWeights;
       
       MPI_Recv( &thisWeights, 1, MPI_DOUBLE, i, MPITag::kDoubleSend,
                MPI_COMM_WORLD, &status );
       totalAccWeights += thisWeights;
       
       // send acknowledgment 
-      MPI_Send( &thisEvents, 1, MPI_LONG, i, MPITag::kAcknowledge,
+      MPI_Send( &thisWeights, 1, MPI_DOUBLE, i, MPITag::kAcknowledge,
                MPI_COMM_WORLD );
     }
     
-    setGenEvents( totalGenEvents );
+    setGenEvents( totalGenWeights );
     setAccEvents( totalAccWeights );
   }
   else{
@@ -134,7 +133,6 @@ NormIntInterfaceMPI::setupMPI()
     // usage on the lead node
     loadMC();
 
-    long int thisEvents;
     double thisWeights;
 
     // if we are not the leader, send generated and accepted events
@@ -145,16 +143,16 @@ NormIntInterfaceMPI::setupMPI()
     // to signal that it is ready to accept numbers of events
 
     // data is irrelevant for this receive
-    MPI_Recv( &thisEvents, 1, MPI_LONG, 0, MPITag::kAcknowledge, MPI_COMM_WORLD,
+    MPI_Recv( &thisWeights, 1, MPI_DOUBLE, 0, MPITag::kAcknowledge, MPI_COMM_WORLD,
               &status );
 
-    thisEvents = numGenEvents();
-    MPI_Send( &thisEvents, 1, MPI_LONG, 0, MPITag::kIntSend, MPI_COMM_WORLD );
+    thisWeights = numGenEvents();
+    MPI_Send( &thisWeights, 1, MPI_DOUBLE, 0, MPITag::kDoubleSend, MPI_COMM_WORLD );
     
     thisWeights = numAccEvents();
     MPI_Send( &thisWeights, 1, MPI_DOUBLE, 0, MPITag::kDoubleSend, MPI_COMM_WORLD );
     
-    MPI_Recv( &thisEvents, 1, MPI_LONG, 0, MPITag::kAcknowledge, MPI_COMM_WORLD,
+    MPI_Recv( &thisWeights, 1, MPI_DOUBLE, 0, MPITag::kAcknowledge, MPI_COMM_WORLD,
              &status );
   }
 }
@@ -185,8 +183,8 @@ NormIntInterfaceMPI::sumIntegrals( IntType type ) const
 
   // now broadcast the total number of events from the leader to the
   // followers so that they may renormalize the sum properly
-  long int totalEvents = numGenEvents();
-  MPI_Bcast( &totalEvents, 1, MPI_LONG, 0, MPI_COMM_WORLD );
+  double totalEvents = numGenEvents();
+  MPI_Bcast( &totalEvents, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD );
   
   // and renormalize the sum
   for( int i = 0; i < cacheSize(); ++i ) result[i] /= totalEvents;