diff --git a/xpcom/glue/nsTArray.h b/xpcom/glue/nsTArray.h
index 98281e68ea71..44c5eeaa7ede 100644
--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -1604,11 +1604,12 @@ public:
   // @param aIndex the place to insert the new elements. This must be no
   //               greater than the current length of the array.
   // @param aCount the number of elements to insert
+  template<typename ActualAlloc = Alloc>
   elem_type* InsertElementsAt(index_type aIndex, size_type aCount)
   {
-    if (!base_type::template InsertSlotsAt<Alloc>(aIndex, aCount,
-                                                  sizeof(elem_type),
-                                                  MOZ_ALIGNOF(elem_type))) {
+    if (!base_type::template InsertSlotsAt<ActualAlloc>(aIndex, aCount,
+                                                        sizeof(elem_type),
+                                                        MOZ_ALIGNOF(elem_type))) {
       return nullptr;
     }
 
@@ -1622,6 +1623,13 @@ public:
     return Elements() + aIndex;
   }
 
+  /* MOZ_WARN_UNUSED_RESULT */
+  elem_type* InsertElementsAt(index_type aIndex, size_type aCount,
+                              const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<FallibleAlloc>(aIndex, aCount);
+  }
+
   // This method inserts elements into the array, constructing them
   // elem_type's copy constructor (or whatever one-arg constructor
   // happens to match the Item type).
@@ -1629,13 +1637,13 @@ public:
   //               greater than the current length of the array.
   // @param aCount the number of elements to insert.
   // @param aItem the value to use when constructing the new elements.
-  template<class Item>
+  template<class Item, typename ActualAlloc = Alloc>
   elem_type* InsertElementsAt(index_type aIndex, size_type aCount,
                               const Item& aItem)
   {
-    if (!base_type::template InsertSlotsAt<Alloc>(aIndex, aCount,
-                                                  sizeof(elem_type),
-                                                  MOZ_ALIGNOF(elem_type))) {
+    if (!base_type::template InsertSlotsAt<ActualAlloc>(aIndex, aCount,
+                                                        sizeof(elem_type),
+                                                        MOZ_ALIGNOF(elem_type))) {
       return nullptr;
     }
 
@@ -1649,6 +1657,14 @@ public:
     return Elements() + aIndex;
   }
 
+  template<class Item>
+  /* MOZ_WARN_UNUSED_RESULT */
+  elem_type* InsertElementsAt(index_type aIndex, size_type aCount,
+                              const Item& aItem, const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<Item, FallibleAlloc>(aIndex, aCount, aItem);
+  }
+
   // This method may be called to minimize the memory used by this array.
   void Compact()
   {