diff --git a/crossenv/flake.nix b/crossenv/flake.nix
index e733c708b111940832d484c96cf6a39d6f38d482..fb083c9d51819eb1649be289bc39ce096445e2c4 100644
--- a/crossenv/flake.nix
+++ b/crossenv/flake.nix
@@ -47,7 +47,8 @@
         };
 
         nativeBuildInputs = [
-          # expose
+          # expose ffi header and library so we can build cffi, itself used by
+          # various other Python packages
           cross-pkgs.libffi
         ];