diff --git a/module.nix b/module.nix
index cff0944..2af7635 100644
--- a/module.nix
+++ b/module.nix
@@ -32,7 +32,7 @@ in
       };
 
       publicKey = lib.mkOption {
-        type = types.nullOr types.path;
+        type = types.nullOr types.str;
         default = null;
         description = ''
           The public key to sign the derivations with.