diff --git a/pkgs/development/haskell-modules/configuration-common.nix b/pkgs/development/haskell-modules/configuration-common.nix
index 3fa77f28ef28..133aa01f0c2e 100644
--- a/pkgs/development/haskell-modules/configuration-common.nix
+++ b/pkgs/development/haskell-modules/configuration-common.nix
@@ -166,9 +166,10 @@ self: super: {
   # https://github.com/lspitzner/czipwith/issues/5
   czipwith = doJailbreak super.czipwith;
 
-  # jacinda needs latest version of alex
+  # jacinda needs latest version of alex and happy
   jacinda = super.jacinda.override {
     alex = self.alex_3_5_1_0;
+    happy = self.happy_2_1_2;
   };
 
   # 2024-07-09: rhine 1.4.* needs newer monad-schedule than stackage (and is only consumer)
diff --git a/pkgs/development/haskell-modules/configuration-nix.nix b/pkgs/development/haskell-modules/configuration-nix.nix
index 4e140b2c5bb7..a677d36820ad 100644
--- a/pkgs/development/haskell-modules/configuration-nix.nix
+++ b/pkgs/development/haskell-modules/configuration-nix.nix
@@ -1327,6 +1327,14 @@ self: super: builtins.intersectAttrs super {
     ] ++ drv.testFlags or [];
   }) super.http-api-data-qq;
 
+  # Test have become more fussy in >= 2.0. We need to have which available for
+  # tests to succeed and the makefile no longer finds happy by itself.
+  happy_2_1_2 = overrideCabal (drv: {
+    buildTools = drv.buildTools or [ ] ++ [ pkgs.buildPackages.which ];
+    preCheck = drv.preCheck or "" + ''
+      export PATH="$PWD/dist/build/happy:$PATH"
+    '';
+  }) super.happy_2_1_2;
   # Additionally install documentation
   jacinda = overrideCabal (drv: {
     enableSeparateDocOutput = true;