diff --git a/nixos/modules/services/x11/display-managers/slim.nix b/nixos/modules/services/x11/display-managers/slim.nix
index 9e8b9391f45f..7ecad3224a99 100644
--- a/nixos/modules/services/x11/display-managers/slim.nix
+++ b/nixos/modules/services/x11/display-managers/slim.nix
@@ -104,9 +104,16 @@ in
         execCmd = "exec ${pkgs.slim}/bin/slim";
       };
 
-    # Allow null passwords so that the user can login as root on the
-    # installation CD.
-    security.pam.services = [ { name = "slim"; allowNullPassword = true; startSession = true; } ];
+    security.pam.services =
+      [ # Allow null passwords so that the user can login as root on the
+        # installation CD.
+        { name = "slim"; allowNullPassword = true; startSession = true; }
+
+        # Allow slimlock to work.
+        { name = "slimlock"; }
+      ];
+
+    environment.systemPackages = [ pkgs.slim ];
 
   };