diff --git a/nixos/tests/gnome3-gdm.nix b/nixos/tests/gnome3-gdm.nix
index 4b459e93e1b..71ae1709d52 100644
--- a/nixos/tests/gnome3-gdm.nix
+++ b/nixos/tests/gnome3-gdm.nix
@@ -26,15 +26,22 @@ import ./make-test.nix ({ pkgs, ...} : {
 
   testScript =
     ''
+      # wait for gdm to start and bring up X
+      $machine->waitForUnit("display-manager.service");
       $machine->waitForX;
-      $machine->sleep(15);
+
+      # wait for alice to be logged in
+      $machine->waitForUnit("default.target","alice");
 
       # Check that logging in has given the user ownership of devices.
       $machine->succeed("getfacl /dev/snd/timer | grep -q alice");
 
-      $machine->succeed("su - alice -c 'DISPLAY=:0.0 gnome-terminal &'");
-      $machine->succeed("xauth merge ~alice/.Xauthority");
+      # open a terminal and check it's there
+      $machine->succeed("su - alice -c 'DISPLAY=:0.0 XAUTHORITY=/run/user/\$UID/gdm/Xauthority gnome-terminal'");
+      $machine->succeed("xauth merge /run/user/1000/gdm/Xauthority");
       $machine->waitForWindow(qr/Terminal/);
+
+      # wait to get a nice screenshot
       $machine->sleep(20);
       $machine->screenshot("screen");
     '';