diff --git a/pkgs/build-support/build-mozilla-mach/default.nix b/pkgs/build-support/build-mozilla-mach/default.nix
index 165c6dff66e0..3f20759e952e 100644
--- a/pkgs/build-support/build-mozilla-mach/default.nix
+++ b/pkgs/build-support/build-mozilla-mach/default.nix
@@ -462,21 +462,7 @@ buildStdenv.mkDerivation {
     # linking firefox hits the vm.max_map_count kernel limit with the default musl allocator
     # TODO: Default vm.max_map_count has been increased, retest without this
     export LD_PRELOAD=${mimalloc}/lib/libmimalloc.so
-  ''
-  +
-    # fileport.h was exposed in SDK 15.4 but we have only 15.2 in nixpkgs so far.
-    lib.optionalString
-      (
-        stdenv.hostPlatform.isDarwin
-        && lib.versionAtLeast version "143"
-        && lib.versionOlder version "145"
-        && lib.versionOlder apple-sdk_15.version "15.4"
-      )
-      ''
-        mkdir -p xnu/sys
-        cp ${apple-sdk_15.sourceRelease "xnu"}/bsd/sys/fileport.h xnu/sys
-        export CXXFLAGS="-isystem $(pwd)/xnu"
-      '';
+  '';
 
   # firefox has a different definition of configurePlatforms from nixpkgs, see configureFlags
   configurePlatforms = [ ];