diff --git a/flake.nix b/flake.nix
index 59ec2ac..bca0e46 100644
--- a/flake.nix
+++ b/flake.nix
@@ -24,7 +24,7 @@
         # working on them.
         src = pkgs.lib.cleanSourceWith {
           src = gitignore.lib.gitignoreSource ./.;
-          filter = path: type: builtins.baseNameOf path != "flake.nix" && builtins.baseNameOf path != "flake.lock" && !(builtins.match "^\\.gitea.*" path);
+          filter = path: type: builtins.baseNameOf path != "flake.nix" && builtins.baseNameOf path != "flake.lock" && builtins.match "^\\.gitea.*" path != null;
         };
 
         # Avoid linking against libc