diff --git a/accessible/src/base/nsDocAccessible.cpp b/accessible/src/base/nsDocAccessible.cpp
index 85874e23800c..e4ec97bb1994 100644
--- a/accessible/src/base/nsDocAccessible.cpp
+++ b/accessible/src/base/nsDocAccessible.cpp
@@ -679,8 +679,10 @@ nsDocAccessible::Shutdown()
     mParent->RemoveChild(this);
   }
 
-  PRUint32 childDocCount = mChildDocuments.Length();
-  for (PRUint32 idx = 0; idx < childDocCount; idx++)
+  // Walk the array backwards because child documents remove themselves from the
+  // array as they are shutdown.
+  PRInt32 childDocCount = mChildDocuments.Length();
+  for (PRInt32 idx = childDocCount - 1; idx >= 0; idx--)
     mChildDocuments[idx]->Shutdown();
 
   mChildDocuments.Clear();