diff --git a/maintainers/scripts/haskell/maintainer-handles.nix b/maintainers/scripts/haskell/maintainer-handles.nix
index 08c6bc4c96afd..d650e82f8b0c1 100644
--- a/maintainers/scripts/haskell/maintainer-handles.nix
+++ b/maintainers/scripts/haskell/maintainer-handles.nix
@@ -1,7 +1,21 @@
 # Nix script to lookup maintainer github handles from their email address. Used by ./hydra-report.hs.
+#
+# This script produces an attr set mapping of email addresses to GitHub handles:
+#
+# ```nix
+# > import ./maintainer-handles.nix
+# { "cdep.illabout@gmail.com" = "cdepillabout"; "john@smith.com" = "johnsmith"; ... }
+# ```
+#
+# This mapping contains all maintainers in ../../mainatainer-list.nix, but it
+# ignores maintainers who don't have a GitHub account or an email address.
 let
   pkgs = import ../../.. {};
   maintainers = import ../../maintainer-list.nix;
   inherit (pkgs) lib;
-  mkMailGithubPair = _: maintainer: if maintainer ? github then { "${maintainer.email}" = maintainer.github; } else {};
+  mkMailGithubPair = _: maintainer:
+    if (maintainer ? email) && (maintainer ? github) then
+      { "${maintainer.email}" = maintainer.github; }
+    else
+      {};
 in lib.zipAttrsWith (_: builtins.head) (lib.mapAttrsToList mkMailGithubPair maintainers)