diff --git a/Generator/src/BeamBackgroundFileParserV1.cpp b/Generator/src/BeamBackgroundFileParserV1.cpp
index a39d2cd332364dce4543b8063ab91bf2c468d5dc..fc17b2ba3e9f2b0ab8fb08e9f5043c4c4d38a5e9 100644
--- a/Generator/src/BeamBackgroundFileParserV1.cpp
+++ b/Generator/src/BeamBackgroundFileParserV1.cpp
@@ -69,8 +69,7 @@ bool BeamBackgroundFileParserV1::load(IBeamBackgroundFileParser::BeamBackgroundD
 bool BeamBackgroundFileParserV1::SampleParticleNum(int& npart, int& start ){
 
   if(m_Nmcp==-1){
-    npart = int(m_rate * m_timewindow);
-    npart = CLHEP::RandPoisson::shoot(npart);
+    npart = int( CLHEP::RandPoisson::shoot(m_rate * m_timewindow) ) ;
   }
   else npart = m_Nmcp;