diff --git a/modules/gui/phosh.nix b/modules/gui/phosh.nix
index bcfdaba0a..3b988ea85 100644
--- a/modules/gui/phosh.nix
+++ b/modules/gui/phosh.nix
@@ -78,6 +78,9 @@ in
     }
     (mkIf cfg.useGreeter {
       services.xserver.enable = true;
+      # NB: setting defaultSession has the critical side-effect that it lets org.freedesktop.AccountsService
+      # know that our user exists. this ensures lightdm succeeds when calling /org/freedesktop/AccountsServices ListCachedUsers
+      services.xserver.displayManager.defaultSession = "sm.puri.Phosh";
       services.xserver.displayManager.lightdm.greeters.gtk.enable = false;  # gtk greeter overrides our own?
       services.xserver.displayManager.lightdm.greeter = {
         enable = true;