diff --git a/corsika/detail/modules/pythia8/Interaction.inl b/corsika/detail/modules/pythia8/Interaction.inl
index 0f09b8a0d4285f38e9cb44c161ab43d53e97b6ce..2b218e11ead447aaa698b888dcbee1bfd1b500cb 100644
--- a/corsika/detail/modules/pythia8/Interaction.inl
+++ b/corsika/detail/modules/pythia8/Interaction.inl
@@ -250,7 +250,7 @@ namespace corsika::pythia8 {
       throw std::runtime_error("invalid target,projectile,energy combination.");
     }
 
-    COMBoost const boost{projectileP4NN, constants::nucleonMass};
+    COMBoost const boost{projectileP4NN, targetP4NN};
     // auto const proj4MomLab = labFrameBoost.toCoM(projectileP4);
     auto const& rotCS = boost.getRotatedCS();
     // auto const pProjLab = proj4MomLab.getSpaceLikeComponents().getComponents(rotCS);