diff --git a/flake.nix b/flake.nix
index fbfe8bf..22902b1 100644
--- a/flake.nix
+++ b/flake.nix
@@ -44,6 +44,15 @@
       perSystem = { self', pkgs, config, ... }: {
         packages.default  = self'.packages.ghc98-binrep;
         devShells.default = self'.devShells.ghc98;
+        haskellProjects.ghc910 = {
+          basePackages = pkgs.haskell.packages.ghc98;
+          # v https://github.com/phadej/defun/pull/5
+          settings.defun-core.jailbreak = true;
+          settings.strongweak.broken = false;
+          settings.text-icu.check = false; # 2025-09-25: one test fails???
+          packages.bytezap.source = inputs.bytezap;
+          devShell = defDevShell "ghc98";
+        };
         haskellProjects.ghc98 = {
           basePackages = pkgs.haskell.packages.ghc98;
           settings.strongweak.broken = false;