diff --git a/layout/html/base/src/nsDST.h b/layout/html/base/src/nsDST.h
index bf7e60f9f99..b76938cce2c 100644
--- a/layout/html/base/src/nsDST.h
+++ b/layout/html/base/src/nsDST.h
@@ -48,7 +48,10 @@ public:
 #endif
 
 private:
+  struct Node;
   struct NodeArena;
+  friend struct Node;       // needs access to struct NodeArena
+  friend struct NodeArena;  // needs access to struct Node
 
   struct Node {
     void* mKey;
@@ -79,9 +82,6 @@ private:
   NodeArena   mArena;
   PtrBits     mLevelZeroBit;
 
-  friend struct Node;       // needs access to struct NodeArena
-  friend struct NodeArena;  // needs access to struct Node
-
 private:
   // Helper functions
   Node** SearchTree(void* aKey) const;