--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -530,19 +530,16 @@ public:
 template<class A, class B>
 class nsDefaultComparator
 {
 public:
   bool Equals(const A& aA, const B& aB) const { return aA == aB; }
   bool LessThan(const A& aA, const B& aB) const { return aA < aB; }
 };
 
-template<class E> class InfallibleTArray;
-template<class E> class FallibleTArray;
-
 template<bool IsPod, bool IsSameType>
 struct AssignRangeAlgorithm
 {
   template<class Item, class ElemType, class IndexType, class SizeType>
   static void implementation(ElemType* aElements, IndexType aStart,
                              SizeType aCount, const Item* aValues)
   {
     ElemType* iter = aElements + aStart;

--- a/xpcom/glue/nsTArrayForwardDeclare.h
+++ b/xpcom/glue/nsTArrayForwardDeclare.h
@@ -25,11 +25,12 @@ template<class E>
 class nsTArray;
 
 template<class E>
 class FallibleTArray;
 
 template<class E, size_t N>
 class AutoTArray;
 
-#define InfallibleTArray nsTArray
+template<class E>
+using InfallibleTArray = nsTArray<E>;
 
 #endif