--- a/daemon/gdm-wayland-session.c
+++ b/daemon/gdm-wayland-session.c
@@ -285,6 +285,7 @@ spawn_session (State        *state,
                                                     "WAYLAND_DISPLAY",
                                                     "WAYLAND_SOCKET",
                                                     "GNOME_SHELL_SESSION_MODE",
+                                                    "__NIXOS_SET_ENVIRONMENT_DONE",
                                                     NULL };
 
         g_debug ("Running wayland session");
--- a/daemon/gdm-x-session.c
+++ b/daemon/gdm-x-session.c
@@ -610,6 +610,7 @@ spawn_session (State        *state,
                                                      "WAYLAND_DISPLAY",
                                                      "WAYLAND_SOCKET",
                                                      "GNOME_SHELL_SESSION_MODE",
+                                                     "__NIXOS_SET_ENVIRONMENT_DONE",
                                                      NULL };
 
         g_debug ("Running X session");