diff --git a/module.nix b/module.nix
index 1a4c706..49375ee 100644
--- a/module.nix
+++ b/module.nix
@@ -136,8 +136,8 @@ in
       ];
 
       extraOptions = lib.mkIf (cfg.globalCacheTTL != null) ''
-        narinfo-cache-negative-ttl ${cfg.globalCacheTTL}
-        narinfo-cache-positive-ttl ${cfg.globalCacheTTL}
+        narinfo-cache-negative-ttl ${toString cfg.globalCacheTTL}
+        narinfo-cache-positive-ttl ${toString cfg.globalCacheTTL}
       '';
     };