diff --git a/include/util.h b/include/util.h
index 171713d4f67c51ca8961aba0453735cac4cd1881..f9093130abf73f8bb4d59643daf625c23782f53e 100644
--- a/include/util.h
+++ b/include/util.h
@@ -86,7 +86,7 @@ namespace util {
       const double px = part.p.x;
       const double py = part.p.y;
       const double pz = part.p.z;
-      const double mass = part.mass;
+      const double mass = 0.;
       return ROOT::Math::PxPyPzMVector{px, py, pz, mass};
     });
     return momenta;