diff --git a/config/common.nix b/config/common.nix
index c91cbb4..06c31f9 100644
--- a/config/common.nix
+++ b/config/common.nix
@@ -20,7 +20,7 @@ with lib;
 
     environment.etc = {
       build-timestamp.text = toString config.instance.build-timestamp;
-      "build-seed.sha1sum".text = "${hashed-build-seed}";
+      "build-seed.sha1sum".source = "${hashed-build-seed}";
     };
   };
 }