diff --git a/Tools/autotest/sim_vehicle.py b/Tools/autotest/sim_vehicle.py
index d04fc5532d..be3cab6c97 100755
--- a/Tools/autotest/sim_vehicle.py
+++ b/Tools/autotest/sim_vehicle.py
@@ -656,7 +656,7 @@ def start_mavproxy(opts, stuff):
     # If running inside of a vagrant guest, then we probably want to forward our mavlink out to the containing host OS
     ports = [p + 10 * cmd_opts.instance for p in [14550,14551]]
     for port in ports:
-        if getpass.getuser() == "vagrant":
+        if os.path.isfile("/ardupilot.vagrant"):
             cmd.extend(["--out", "10.0.2.2:" + str(port)])
         else:
             cmd.extend(["--out", "127.0.0.1:" + str(port)])
diff --git a/Tools/vagrant/initvagrant.sh b/Tools/vagrant/initvagrant.sh
index 81efbfad92..2a00a4142d 100755
--- a/Tools/vagrant/initvagrant.sh
+++ b/Tools/vagrant/initvagrant.sh
@@ -82,5 +82,8 @@ cd jsbsim
 make -j2
 EOF
 
+#Plant a marker for sim_vehicle that we're inside a vagrant box
+touch /ardupilot.vagrant
+
 # Now you can run
 # vagrant ssh -c "screen -d -R"