diff --git a/pkgs/by-name/em/emmy-lua-code-style/package.nix b/pkgs/by-name/em/emmy-lua-code-style/package.nix
index 0df147419dc4..7cf1f72aafd1 100644
--- a/pkgs/by-name/em/emmy-lua-code-style/package.nix
+++ b/pkgs/by-name/em/emmy-lua-code-style/package.nix
@@ -19,6 +19,9 @@ stdenv.mkDerivation (finalAttrs: {
 
   nativeBuildInputs = [ cmake ];
 
+  # Vendored mimalloc-2.0.9 uses ATOMIC_VAR_INIT, removed in C23.
+  env.NIX_CFLAGS_COMPILE = "-std=gnu17";
+
   passthru.updateScript = nix-update-script { };
 
   meta = {