diff --git a/Processes/Pythia/Interaction.cc b/Processes/Pythia/Interaction.cc
index 70565f0f82d793f028b520dcd849f99de9215b39..d7f04a0af203aae749b65ceec5872160759f55af 100644
--- a/Processes/Pythia/Interaction.cc
+++ b/Processes/Pythia/Interaction.cc
@@ -150,7 +150,7 @@ namespace corsika::process::pythia {
           const double sigEla = fSigma.sigmaEl();
           const double sigProd = fSigma.sigmaTot() - sigEla;
 
-          return std::make_tuple(sigProd * 1_mb, sigEla * 1_mb);
+          return std::make_tuple(sigProd * (1_fm * 1_fm), sigEla * (1_fm * 1_fm));
 
         } else
           throw std::runtime_error("pythia cross section init failed");