diff --git a/gnu/services/xorg.scm b/gnu/services/xorg.scm
index e43bfcffe048bec892153c86711caba2e9e70bc2..7c875a1ae11b331c80cf8ee2581475d8501d5f86 100644
--- a/gnu/services/xorg.scm
+++ b/gnu/services/xorg.scm
@@ -246,7 +246,9 @@ (define* (slim-service #:key (slim slim)
 theme."
 
   (define (slim.cfg)
-    (mlet %store-monad ((startx  (or startx (xorg-start-command)))
+    (mlet %store-monad ((startx  (if startx
+                                     (return startx)
+                                     (xorg-start-command)))
                         (xinitrc (xinitrc #:fallback-session
                                           auto-login-session)))
       (text-file* "slim.cfg"  "