diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index 93c2727b6679..cb20e780c6be 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -2234,19 +2234,23 @@ IsContextOnStack(nsIJSContextStack *aStack, JSContext *aContext)
     return PR_FALSE;
   if (ctx == aContext)
     return PR_TRUE;
-  
+
   nsCOMPtr<nsIJSContextStackIterator>
     iterator(do_CreateInstance("@mozilla.org/js/xpc/ContextStackIterator;1"));
   NS_ENSURE_TRUE(iterator, PR_FALSE);
 
   nsresult rv = iterator->Reset(aStack);
   NS_ENSURE_SUCCESS(rv, PR_FALSE);
-  
+
   PRBool done;
   while (NS_SUCCEEDED(iterator->Done(&done)) && !done) {
     rv = iterator->Prev(&ctx);
     NS_ASSERTION(NS_SUCCEEDED(rv), "Broken iterator implementation");
 
+    if (!ctx) {
+      continue;
+    }
+
     if (nsJSUtils::GetDynamicScriptContext(ctx) && ctx == aContext)
       return PR_TRUE;
   }
diff --git a/dom/src/base/nsLocation.cpp b/dom/src/base/nsLocation.cpp
index 99933f9b39b1..edfd3739c09d 100644
--- a/dom/src/base/nsLocation.cpp
+++ b/dom/src/base/nsLocation.cpp
@@ -82,12 +82,17 @@ GetContextFromStack(nsIJSContextStack *aStack, JSContext **aContext)
 
   nsresult rv = iterator->Reset(aStack);
   NS_ENSURE_SUCCESS(rv, rv);
-  
+
   PRBool done;
   while (NS_SUCCEEDED(iterator->Done(&done)) && !done) {
     rv = iterator->Prev(aContext);
     NS_ASSERTION(NS_SUCCEEDED(rv), "Broken iterator implementation");
 
+    // Consider a null context the end of the line.
+    if (!*aContext) {
+      break;
+    }
+
     if (nsJSUtils::GetDynamicScriptContext(*aContext)) {
       return NS_OK;
     }