diff --git a/overlay.nix b/overlay.nix
index 112ca8f..9cc6df6 100644
--- a/overlay.nix
+++ b/overlay.nix
@@ -31,6 +31,12 @@ final: prev:
     filesToInstall = ["u-boot.bin" "u-boot"];
   };
 
+  # To cross compile for riscv64, we need to populate this env variable, not
+  # NIX_CFLAGS_COMPILE, otherwise we affect the packages for x86.
+  stdenv = prev.stdenvAdapters.addAttrsToDerivation {
+    NIX_CFLAGS_COMPILE_riscv64_unknown_linux_gnu = "-march=rv64g";
+  } prev.stdenv;
+
   opensbi-uboot = prev.opensbi.overrideAttrs (old: {
     makeFlags = old.makeFlags ++ [
         # Build OpenSBI without compressed instructions