diff --git a/prodtests/full_system_test.sh b/prodtests/full_system_test.sh
index 5c7157f93c652..e8b298cc08d8c 100755
--- a/prodtests/full_system_test.sh
+++ b/prodtests/full_system_test.sh
@@ -67,7 +67,7 @@ if [[ $BEAMTYPE == "PbPb" ]]; then
 else
   FST_GENERATOR=${FST_GENERATOR:-pythia8pp}
   FST_COLRATE=${FST_COLRATE:-400000}
-  RUNNUMBER=303000 # a default un-anchored pp run number
+  RUNNUMBER=${RUNNUMBER:-303000} # a default un-anchored pp run number
 fi
 FST_MC_ENGINE=${FST_MC_ENGINE:-TGeant4}
 FST_EMBEDDING_CONFIG=${FST_EMBEDDING_CONFIG:-GeneratorPythia8.config=$O2_ROOT/prodtests/full-system-test/pythia8.cfg}
@@ -107,7 +107,7 @@ if [[ $BEAMTYPE == "PbPb" && -z $FST_QED ]]; then
   FST_QED=1
 fi
 DIGIQED=
-SIMOPTKEY="Diamond.width[2]=6.;"
+SIMOPTKEY+="Diamond.width[2]=6.;"
 if [[ $FST_QED == 1 ]]; then
   mkdir -p qed
   cd qed