diff --git a/mozilla/content/base/src/nsContentIterator.cpp b/mozilla/content/base/src/nsContentIterator.cpp
index 206e6e55421..85a6a6ee6d1 100644
--- a/mozilla/content/base/src/nsContentIterator.cpp
+++ b/mozilla/content/base/src/nsContentIterator.cpp
@@ -896,7 +896,7 @@ nsresult nsContentSubtreeIterator::Init(nsIDOMRange* aRange)
   if (!firstCandidate)
   {
     // then firstCandidate is next node after cN
-    if (NS_FAILED(GetNextSibling(cN,  &firstCandidate)))
+    if (NS_FAILED(GetNextSibling(cN,  &firstCandidate)) || !firstCandidate)
     {
       MakeEmpty();
       return NS_OK;
diff --git a/mozilla/layout/base/src/nsContentIterator.cpp b/mozilla/layout/base/src/nsContentIterator.cpp
index 206e6e55421..85a6a6ee6d1 100644
--- a/mozilla/layout/base/src/nsContentIterator.cpp
+++ b/mozilla/layout/base/src/nsContentIterator.cpp
@@ -896,7 +896,7 @@ nsresult nsContentSubtreeIterator::Init(nsIDOMRange* aRange)
   if (!firstCandidate)
   {
     // then firstCandidate is next node after cN
-    if (NS_FAILED(GetNextSibling(cN,  &firstCandidate)))
+    if (NS_FAILED(GetNextSibling(cN,  &firstCandidate)) || !firstCandidate)
     {
       MakeEmpty();
       return NS_OK;