diff --git a/pkgs/by-name/mc/mctc-lib/package.nix b/pkgs/by-name/mc/mctc-lib/package.nix
index 41a09bf7261e..6883ac8a7e6a 100644
--- a/pkgs/by-name/mc/mctc-lib/package.nix
+++ b/pkgs/by-name/mc/mctc-lib/package.nix
@@ -61,6 +61,10 @@ stdenv.mkDerivation rec {
 
   doCheck = true;
 
+  preCheck = ''
+    export OMP_NUM_THREADS=2
+  '';
+
   postPatch = ''
     patchShebangs --build config/install-mod.py
   '';