--- a/nss/build.sh
+++ b/nss/build.sh
@@ -66,6 +66,7 @@
 sslkeylogfile=1
 
 gyp_params=(--depth="$cwd" --generator-output=".")
+gyp_flavor=
 ninja_params=()
 
 # Assume that MSVC is wanted if this is running on windows.
@@ -134,6 +135,7 @@
         --mozilla-central) gyp_params+=(-Dmozilla_central=1) ;;
 	--python) python="$2"; shift ;;
 	--python=*) python="${1#*=}" ;;
+        -DOS=*) gyp_params+=("$1"); gyp_flavor="${1#-DOS=}" ;;
         -D*) gyp_params+=("$1") ;;
         *) show_help; exit 2 ;;
     esac
@@ -275,7 +277,14 @@
         set_nspr_path "$obj_dir/include/nspr:$obj_dir/lib"
     fi
 
-    run_verbose run_scanbuild ${GYP} -f ninja "${gyp_params[@]}" "$cwd/nss.gyp"
+    # On macOS, gyp defaults to "mac" flavor which emits Xcode-specific flags
+    # and tools (libtool, -arch, etc.) incompatible with cross-compilation targets.
+    gyp_format=ninja
+    if [ "$(uname -s)" = "Darwin" ] && [ -n "$gyp_flavor" ] && [ "$gyp_flavor" != "mac" ]; then
+        gyp_format="ninja-${gyp_flavor}"
+        export GYP_CROSSCOMPILE=1
+    fi
+    run_verbose run_scanbuild ${GYP} -f "$gyp_format" "${gyp_params[@]}" "$cwd/nss.gyp"
 
     mv -f "$gyp_config.new" "$gyp_config"
 fi