--- a/layout/style/StyleBackendType.h
+++ b/layout/style/StyleBackendType.h
@@ -7,17 +7,17 @@
 #ifndef mozilla_StyleBackendType_h
 #define mozilla_StyleBackendType_h
 
 namespace mozilla {
 
 /**
  * Enumeration that represents one of the two supported style system backends.
  */
-enum class StyleBackendType : int
+enum class StyleBackendType : uint8_t
 {
   Gecko = 1,
   Servo
 };
 
 } // namespace mozilla
 
 #endif // mozilla_StyleBackendType_h