diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index fc2c008be0c..77bde5c85b7 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -78,6 +78,7 @@ in
   # same package in the (recursive) dependencies of the package being
   # built. Will delay failures, if any, to compile time.
   allowInconsistentDependencies ? false
+, maxBuildCores ? 4 # GHC usually suffers beyond -j4. https://ghc.haskell.org/trac/ghc/ticket/9221
 } @ args:
 
 assert editedCabalFile != null -> revision != null;
@@ -250,6 +251,7 @@ stdenv.mkDerivation ({
   '' + postPatch;
 
   setupCompilerEnvironmentPhase = ''
+    NIX_BUILD_CORES=$(( NIX_BUILD_CORES < ${toString maxBuildCores} ? NIX_BUILD_CORES : ${toString maxBuildCores} ))
     runHook preSetupCompilerEnvironment
 
     echo "Build with ${ghc}."