diff --git a/nix/culr-module.nix b/nix/culr-module.nix
index 389d99f..0e2c066 100644
--- a/nix/culr-module.nix
+++ b/nix/culr-module.nix
@@ -24,8 +24,8 @@ in {
   config = mkIf cfg.enable {
     environment.systemPackages = let inherit (pkgs) culr; in [culr];
     environment.sessionVariables = {
-      CULR_PATTERN = mkIf cfg.pattern cfg.pattern;
-      CULR_PALETTE = mkIf cfg.palette cfg.palette;
+      CULR_PATTERN = mkIf (cfg.pattern != null) cfg.pattern;
+      CULR_PALETTE = mkIf (cfg.palette != null) cfg.palette;
     };
   };
 }