diff --git a/xpcom/glue/nsTArray.h b/xpcom/glue/nsTArray.h
index 8f7f3c77a78c..db0c98119455 100644
--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -1284,6 +1284,11 @@ class nsAutoTArray : public nsAutoArrayBase<nsTArray<E, Alloc>, N>
 {
 public:
   nsAutoTArray() {}
+
+  template<typename Allocator>
+  nsAutoTArray(const nsTArray<E, Allocator>& other) {
+    AppendElements(other);
+  }
 };
 
 template<class E, PRUint32 N>
@@ -1291,6 +1296,11 @@ class AutoFallibleTArray : public nsAutoArrayBase<FallibleTArray<E>, N>
 {
 public:
   AutoFallibleTArray() {}
+
+  template<typename Allocator>
+  AutoFallibleTArray(const nsTArray<E, Allocator>& other) {
+    AppendElements(other);
+  }
 };
 
 #if defined(MOZALLOC_HAVE_XMALLOC)
@@ -1299,6 +1309,11 @@ class AutoInfallibleTArray : public nsAutoArrayBase<InfallibleTArray<E>, N>
 {
 public:
   AutoInfallibleTArray() {}
+
+  template<typename Allocator>
+  AutoInfallibleTArray(const nsTArray<E, Allocator>& other) {
+    AppendElements(other);
+  }
 };
 #endif