diff --git a/Processes/UrQMD/UrQMD.cc b/Processes/UrQMD/UrQMD.cc
index 4caedb88c934dc5e1ff63ba18791f437b06f9e3d..adee6aafc98b512b781f569976443b87efb7f140 100644
--- a/Processes/UrQMD/UrQMD.cc
+++ b/Processes/UrQMD/UrQMD.cc
@@ -92,9 +92,8 @@ corsika::process::EProcessReturn UrQMD::DoInteraction(SetupProjectile& projectil
     cascinit_(sys_.Zp, sys_.Ap, id);
   } else {
     inputs_.prspflg = 1;
-    int const Ap =
-        1; // what value to use here for non-baryons??? see CONEX UrQMD interface
-    rsys_.bdist = nucrad_(Ap) + nucrad_(Atarget) + 2 * options_.CTParam[30 - 1];
+    sys_.Ap = 1; // even for non-baryons this has to be set, see vanilla UrQMD.f
+    rsys_.bdist = nucrad_(sys_.Ap) + nucrad_(Atarget) + 2 * options_.CTParam[30 - 1];
 
     auto const [ityp, iso3] = ConvertToUrQMD(projectileCode);
     // todo: conversion of K_long/short into strong eigenstates;