diff --git a/layout/style/UserAgentStyleSheetID.h b/layout/style/UserAgentStyleSheetID.h
new file mode 100644
index 000000000000..58de5cc60742
--- /dev/null
+++ b/layout/style/UserAgentStyleSheetID.h
@@ -0,0 +1,23 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* an identifier for User Agent style sheets */
+
+#ifndef mozilla_UserAgentStyleSheetID_h
+#define mozilla_UserAgentStyleSheetID_h
+
+namespace mozilla {
+
+enum class UserAgentStyleSheetID : uint8_t {
+#define STYLE_SHEET(identifier_, url_, shared_) identifier_,
+#include "mozilla/UserAgentStyleSheetList.h"
+#undef STYLE_SHEET
+  Count
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_UserAgentStyleSheetID_h
diff --git a/layout/style/moz.build b/layout/style/moz.build
index 2162175305d1..36e1c8b3dbd4 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -111,6 +111,7 @@ EXPORTS.mozilla += [
     'StyleSheetInfo.h',
     'StyleSheetInlines.h',
     'URLExtraData.h',
+    'UserAgentStyleSheetID.h',
     'UserAgentStyleSheetList.h',
 ]