diff --git a/nixos/modules/config/fonts/fontconfig-ultimate.nix b/nixos/modules/config/fonts/fontconfig-ultimate.nix
index 1bf9fdb19845..c7654ca78c3a 100644
--- a/nixos/modules/config/fonts/fontconfig-ultimate.nix
+++ b/nixos/modules/config/fonts/fontconfig-ultimate.nix
@@ -53,7 +53,7 @@ in
           };
 
           substitutions = mkOption {
-            type = types.nullOr (types.enum ["free" "combi" "ms"]);
+            type = types.enum ["free" "combi" "ms" "none"];
             default = "free";
             description = ''
               Font substitutions to replace common Type 1 fonts with nicer