diff --git a/layout/base/nsIPresShell.h b/layout/base/nsIPresShell.h
index 8fa0b4c82669..4eef66573abb 100644
--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -78,7 +78,7 @@ class nsARefreshObserver;
 class nsAccessibilityService;
 #endif
 class nsIWidget;
-class nsArenaMemoryStats;
+struct nsArenaMemoryStats;
 
 typedef short SelectionType;
 typedef PRUint64 nsFrameState;
diff --git a/layout/base/nsPresArena.h b/layout/base/nsPresArena.h
index 730a05ef5766..78cb0dc9e9d3 100644
--- a/layout/base/nsPresArena.h
+++ b/layout/base/nsPresArena.h
@@ -13,7 +13,7 @@
 
 #include "mozilla/StandardInteger.h"
 
-class nsArenaMemoryStats;
+struct nsArenaMemoryStats;
 
 // Uncomment this to disable arenas, instead forwarding to
 // malloc for every allocation.