diff --git a/nixos/modules/services/torrent/transmission.nix b/nixos/modules/services/torrent/transmission.nix
index 497297ba693a..5dd02eb33163 100644
--- a/nixos/modules/services/torrent/transmission.nix
+++ b/nixos/modules/services/torrent/transmission.nix
@@ -294,7 +294,7 @@ in
       requires = optional apparmor.enable "apparmor.service";
       wantedBy = [ "multi-user.target" ];
       environment.CURL_CA_BUNDLE = etc."ssl/certs/ca-certificates.crt".source;
-      environment.TRANSMISSION_WEB_HOME = lib.optionalString (cfg.webHome != null) cfg.webHome;
+      environment.TRANSMISSION_WEB_HOME = lib.mkIf (cfg.webHome != null) cfg.webHome;
 
       serviceConfig = {
         # Use "+" because credentialsFile may not be accessible to User= or Group=.