diff --git a/benchmarks/dvmp/analysis/dvmp.h b/benchmarks/dvmp/analysis/dvmp.h
index 1784c289dd9d1cdc4b3969692fde6fabe289b18d..5c743eae3b404b80cb81e2b8aa7155f9df2eb00a 100644
--- a/benchmarks/dvmp/analysis/dvmp.h
+++ b/benchmarks/dvmp/analysis/dvmp.h
@@ -209,6 +209,7 @@ namespace util {
   {
     //0:e0  1:p0    2:e1    3:p1    4:recoil system (without p1)    5:l1 from 4 6:l2 from 4
     ROOT::Math::PxPyPzMVector q(parts[0] - parts[2]);
+    ROOT::Math::PxPyPzMVector k(parts[0]);
     ROOT::Math::PxPyPzMVector P(parts[1]);
     ROOT::Math::PxPyPzMVector Delta(parts[3] - parts[1]);//exact
     ROOT::Math::PxPyPzMVector Delta_prime(parts[0] - parts[2] - parts[5] - parts[6]);//exclude gamma radiation in jpsi decay
@@ -221,7 +222,7 @@ namespace util {
     //}else{
         t = Delta.Dot(Delta);
     //}
-    double y = q.Dot(P) / parts[0].Dot(P);
+    double y = q.Dot(P) / k.Dot(P);
     inv_quant quantities = {nu, Q2, Q2/2./P.mass()/nu, y, t};
     return quantities;
   }