diff --git a/nixos/modules/security/pam.nix b/nixos/modules/security/pam.nix
index 9a6c7d178257..5400ba1ef989 100644
--- a/nixos/modules/security/pam.nix
+++ b/nixos/modules/security/pam.nix
@@ -828,7 +828,7 @@ in
       };
       challengeResponsePath = mkOption {
         default = null;
-        type = types.path;
+        type = types.nullOr types.path;
         description = ''
           If not null, set the path used by yubico pam module where the challenge expected response is stored.