diff --git a/NPLib/Physics/NPReaction.cxx b/NPLib/Physics/NPReaction.cxx
index e420fd67a6af3f6e597a9d7fa10f07c39d6b3b7c..d4a5bf8709193bf8a27eabaa19fc413e43d7ef1a 100644
--- a/NPLib/Physics/NPReaction.cxx
+++ b/NPLib/Physics/NPReaction.cxx
@@ -524,7 +524,7 @@ void Reaction::initializePrecomputeVariable(){
   m2 = fNuclei2->Mass();
   m3 = fNuclei3->Mass() + fExcitation3;
   m4 = fNuclei4->Mass() + fExcitation4;
-  fQValue =fNuclei1->Mass()+fNuclei2->Mass()-fNuclei3->Mass()-fNuclei4->Mass();
+  fQValue =m1+m2-m3-m4;
   
   s = m1*m1 + m2*m2 + 2*m2*(fBeamEnergy + m1);
   fTotalEnergyImpulsionCM = TLorentzVector(0,0,0,sqrt(s));