diff --git a/pkgs/by-name/mo/moltenvk/package.nix b/pkgs/by-name/mo/moltenvk/package.nix
index 6651f2298a2d..4fd4aa6e6b3b 100644
--- a/pkgs/by-name/mo/moltenvk/package.nix
+++ b/pkgs/by-name/mo/moltenvk/package.nix
@@ -101,8 +101,8 @@ stdenv.mkDerivation (finalAttrs: {
   '';
 
   env.NIX_CFLAGS_COMPILE = toString (
-    [
-      "-isystem ${lib.getInclude stdenv.cc.libcxx}/include/c++/v1"
+    lib.optional (stdenv.cc.libcxx != null) "-isystem ${lib.getInclude stdenv.cc.libcxx}/include/c++/v1"
+    ++ [
       "-I${lib.getDev spirv-cross}/include/spirv_cross"
       "-I${lib.getDev spirv-headers}/include/spirv/unified1"