diff --git a/pkgs/development/haskell-modules/configuration-common.nix b/pkgs/development/haskell-modules/configuration-common.nix
index 2cd0a70e57c9..c760829510ff 100644
--- a/pkgs/development/haskell-modules/configuration-common.nix
+++ b/pkgs/development/haskell-modules/configuration-common.nix
@@ -704,13 +704,6 @@ with haskellLib;
           --replace-fail 'InstallDesktopFile $(PREFIX)/bin/git-annex' \
                          'InstallDesktopFile git-annex'
       '';
-
-      # Work around race condition in test suite exposed by tasty-1.5.4
-      # TODO(@sternenseemann): make testFlags arg usable with git-annex
-      preCheck = ''
-        ${drv.preCheck or ""}
-        appendToVar checkFlags -j1
-      '';
     }))
   ];
 
diff --git a/pkgs/development/haskell-modules/configuration-nix.nix b/pkgs/development/haskell-modules/configuration-nix.nix
index eae4e1c104f6..ab279e0a1a63 100644
--- a/pkgs/development/haskell-modules/configuration-nix.nix
+++ b/pkgs/development/haskell-modules/configuration-nix.nix
@@ -1272,6 +1272,8 @@ builtins.intersectAttrs super {
           ln -sf git-annex git-remote-tor-annex
           PATH+=":$PWD"
 
+          checkFlagsArray+=("-J$NIX_BUILD_CORES")
+
           echo checkFlags: $checkFlags ''${checkFlagsArray:+"''${checkFlagsArray[@]}"}
 
           # Doesn't use Cabal's test mechanism