diff --git a/modules/time/default.nix b/modules/time/default.nix
index 28724a55..01c4703b 100644
--- a/modules/time/default.nix
+++ b/modules/time/default.nix
@@ -7,7 +7,7 @@ let
   cfg = config.time;
 
   timeZone = optionalString (cfg.timeZone != null) ''
-    if [ -z $(systemsetup -listtimezones | grep "^ ${cfg.timeZone}$") ]; then
+    if ! systemsetup -listtimezones | grep -q "^ ${cfg.timeZone}$"; then
       echo "${cfg.timeZone} is not a valid timezone. The command 'listtimezones' will show a list of valid time zones." >&2
       false
     fi