diff --git a/pkgs/development/haskell-modules/configuration-ghc-8.10.x.nix b/pkgs/development/haskell-modules/configuration-ghc-8.10.x.nix
index 736f1a59d6fc..0ec47558bec1 100644
--- a/pkgs/development/haskell-modules/configuration-ghc-8.10.x.nix
+++ b/pkgs/development/haskell-modules/configuration-ghc-8.10.x.nix
@@ -100,6 +100,7 @@ self: super: {
   stylish-haskell = doJailbreak super.stylish-haskell;
 
   # Agda 2.6.1.2 only declares a transformers dependency for ghc < 8.10.3.
+  # https://github.com/agda/agda/issues/5109
   Agda = appendPatch super.Agda (pkgs.fetchpatch {
     url = "https://github.com/agda/agda/commit/76278c23d447b49f59fac581ca4ac605792aabbc.patch";
     sha256 = "1g34g8a09j73h89pk4cdmri0nb0qg664hkff45amcr9kyz14a9f3";