diff --git a/pkgs/development/libraries/haskell/either/default.nix b/pkgs/development/libraries/haskell/either/default.nix
index bfc0f4c593b..93dfd043c90 100644
--- a/pkgs/development/libraries/haskell/either/default.nix
+++ b/pkgs/development/libraries/haskell/either/default.nix
@@ -3,8 +3,8 @@
 
 cabal.mkDerivation (self: {
   pname = "either";
-  version = "3.4.2";
-  sha256 = "0h5hrjvcbgyn0fpn6xlm2a4447xl4qyhiadq2vlywqvkvgnh3x3k";
+  version = "4.0";
+  sha256 = "07axaq43cqyglndr5az7ns4mvkjmybq6z8s32l1jxc5x7532scwr";
   buildDepends = [
     MonadRandom mtl semigroupoids semigroups transformers
   ];