diff --git a/home/common.nix b/home/common.nix
index f65ceff..92cee82 100644
--- a/home/common.nix
+++ b/home/common.nix
@@ -51,7 +51,7 @@
       merge.tool = "vimdiff";
       # provide `git mergetool -t nixfmt`
       mergetool.nixfmt = {
-        cmd = "${lib.getExe pkgs.nixfmt-rfc-style} --mergetool \"$BASE\" \"$LOCAL\" \"$REMOTE\" \"$MERGED\"";
+        cmd = "${lib.getExe inputs.nixos-unstable.legacyPackages.${system}.nixfmt-rfc-style} --mergetool \"$BASE\" \"$LOCAL\" \"$REMOTE\" \"$MERGED\"";
         trustExitCode = true;
       };
       core.excludesfile = toString (