diff --git a/Generators/Pythia8_i/src/Pythia8_i.cxx b/Generators/Pythia8_i/src/Pythia8_i.cxx
index fc1afb074c0c8e09268709d83f997023c20867f6..f3e7869bae19ec4a80cbf584142eeb7034af615d 100644
--- a/Generators/Pythia8_i/src/Pythia8_i.cxx
+++ b/Generators/Pythia8_i/src/Pythia8_i.cxx
@@ -36,11 +36,11 @@ using boost::assign::operator+=;
   #undef PYTHIA8_NWEIGHTS
   #undef PYTHIA8_WEIGHT
   #undef PYTHIA8_WLABEL
-  #undef PYTHIA8_CONVERSION
   #define PYTHIA8_NWEIGHTS nVariationGroups
   #define PYTHIA8_WEIGHT getGroupWeight
   #define PYTHIA8_WLABEL getGroupName
   #if PYTHIA_VERSION_INTEGER < 8244
+    #undef PYTHIA8_CONVERSION
     #define PYTHIA8_CONVERSION 1.0e9
   #endif 
   #endif