diff --git a/layout/base/nsStyleSheetService.h b/layout/base/nsStyleSheetService.h
index 83fc829aad19f8b80692e67bddb781778fbc4f8d..04806a1f51686a82c1dc2555dae86a4397b181fb 100644
--- a/layout/base/nsStyleSheetService.h
+++ b/layout/base/nsStyleSheetService.h
@@ -50,6 +50,8 @@ class nsStyleSheetService final : public nsIStyleSheetService,
 
   size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
 
+  void ZenMarkStylesAsChanged();
+
   static nsStyleSheetService* GetInstance();
   static nsStyleSheetService* gInstance;
 
