diff --git a/layout/style/nsCSSStyleSheet.h b/layout/style/nsCSSStyleSheet.h
index c39b08a6a6a2..995bf31a6c4e 100644
--- a/layout/style/nsCSSStyleSheet.h
+++ b/layout/style/nsCSSStyleSheet.h
@@ -64,6 +64,10 @@ class nsCSSStyleSheet;
 
 class nsCSSStyleSheetInner {
 public:
+  friend class nsCSSStyleSheet;
+  friend class nsCSSRuleProcessor;
+  friend nsresult NS_NewCSSStyleSheet(nsICSSStyleSheet** aInstancePtrResult);
+private:
   nsCSSStyleSheetInner(nsICSSStyleSheet* aPrimarySheet);
   nsCSSStyleSheetInner(nsCSSStyleSheetInner& aCopy,
                        nsCSSStyleSheet* aPrimarySheet);