diff --git a/forward_ions.cxx b/forward_ions.cxx
index 4b42997a71c0abacc9152e78f4f78c3ccc657020..5c7a6090d3c4da6182bbdb494c3fb168c3b60bb6 100644
--- a/forward_ions.cxx
+++ b/forward_ions.cxx
@@ -13,7 +13,7 @@ void forward_ions(){
   WriterAscii hepmc_output("data/forward_ions.hepmc");
   int        events_parsed = 0;
   GenEvent   evt(Units::GEV, Units::MM);
-  std::mt19937 gen(1337);
+  std::mt19937 gen( std::stoi(std::getenv("SEED")) );
   std::uniform_real_distribution<double> phi_distr(0,6.2831853072);
   std::uniform_real_distribution<double> theta_distr(0,0.01745329252);
 
diff --git a/setup.sh b/setup.sh
new file mode 100644
index 0000000000000000000000000000000000000000..91f9519859a3d300b6ce279fef48e8409b675369
--- /dev/null
+++ b/setup.sh
@@ -0,0 +1 @@
+export SEED="1337"