diff --git a/README.md b/README.md
index 2038d39..3261cff 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,7 @@
 
 On a NIX machine:
 ```bash
+export NIX_BUILD_CORES=0
 nix-build '<nixpkgs/nixos>' -A config.system.build.kernel --arg configuration ./custom-kernel.nix
 ```