diff --git a/pkgs/os-specific/linux/virtualbox/default.nix b/pkgs/os-specific/linux/virtualbox/default.nix
index f6846eb1945d..2c30499c23f9 100644
--- a/pkgs/os-specific/linux/virtualbox/default.nix
+++ b/pkgs/os-specific/linux/virtualbox/default.nix
@@ -16,7 +16,7 @@ stdenv.mkDerivation {
 
   nativeBuildInputs = kernel.moduleBuildDependencies;
 
-  KERN_DIR = "${kernel.dev}/lib/modules/${kernel.modDirVersion}/build";
+  env.KERN_DIR = "${kernel.dev}/lib/modules/${kernel.modDirVersion}/build";
 
   makeFlags = [ "INSTALL_MOD_PATH=$(out)" ];
   installTargets = [ "install" ];