diff --git a/pkgs/tools/misc/file/default.nix b/pkgs/tools/misc/file/default.nix
index 6454bb4eac28..9b982f2c2eac 100644
--- a/pkgs/tools/misc/file/default.nix
+++ b/pkgs/tools/misc/file/default.nix
@@ -1,5 +1,10 @@
 { lib, stdenv, fetchurl, file, zlib, libgnurx }:
 
+# Note: this package is used for bootstrapping fetchurl, and thus
+# cannot use fetchpatch! All mutable patches (generated by GitHub or
+# cgit) that are needed here should be included directly in Nixpkgs as
+# files.
+
 stdenv.mkDerivation rec {
   pname = "file";
   version = "5.41";