diff --git a/nixos/modules/services/networking/ntp/chrony.nix b/nixos/modules/services/networking/ntp/chrony.nix
index 5e05a327a3f..96c6444c23a 100644
--- a/nixos/modules/services/networking/ntp/chrony.nix
+++ b/nixos/modules/services/networking/ntp/chrony.nix
@@ -82,6 +82,7 @@ in
       };
 
       initstepslew = mkOption {
+        type = types.attrsOf (types.either types.bool types.int);
         default = {
           enabled = true;
           threshold = 1000; # by default, same threshold as 'ntpd -g' (1000s)