diff --git a/flake.nix b/flake.nix
index fd06ef7df7cf6a96e865dbf1c7b95f1947bdbe50..ed63c1f3ae689ee7714e3c15a9998616c45aee5f 100644
--- a/flake.nix
+++ b/flake.nix
@@ -36,6 +36,12 @@
       devShells = hslib.devShells {
         extraBuildInputs = pkgs:
           with pkgs; [
+            # We configure cabal to use zlib:pkg-config so we better supply
+            # pkg-config in the dev shell or `cabal ...` builds will surely
+            # fail.
+            pkg-config
+
+            # And also that pesky zlib dependency.
             zlib
           ];
       };