diff --git a/mozilla/accessible/src/base/nsAccessibilityService.cpp b/mozilla/accessible/src/base/nsAccessibilityService.cpp
index be0ca1d2174..8e2309cf381 100644
--- a/mozilla/accessible/src/base/nsAccessibilityService.cpp
+++ b/mozilla/accessible/src/base/nsAccessibilityService.cpp
@@ -1044,7 +1044,10 @@ NS_IMETHODIMP
 nsAccessibilityService::GetStringEventType(PRUint32 aEventType,
                                            nsAString& aString)
 {
-  if ( aEventType >= NS_ARRAY_LENGTH(kEventTypeNames)) {
+  NS_ASSERTION(nsIAccessibleEvent::EVENT_LAST_ENTRY == NS_ARRAY_LENGTH(kEventTypeNames),
+               "nsIAccessibleEvent constants are out of sync to kEventTypeNames");
+
+  if (aEventType >= NS_ARRAY_LENGTH(kEventTypeNames)) {
     aString.AssignLiteral("unknown");
     return NS_OK;
   }
diff --git a/mozilla/accessible/src/base/nsAccessibilityService.h b/mozilla/accessible/src/base/nsAccessibilityService.h
index 42704ef2b27..837aa7a6f33 100644
--- a/mozilla/accessible/src/base/nsAccessibilityService.h
+++ b/mozilla/accessible/src/base/nsAccessibilityService.h
@@ -350,6 +350,7 @@ static const char kEventTypeNames[][40] = {
   "hypertext changed",                       // EVENT_HYPERTEXT_CHANGED
   "hypertext links count changed",           // EVENT_HYPERTEXT_NLINKS_CHANGED
   "object attribute changed",                // EVENT_OBJECT_ATTRIBUTE_CHANGED
+  "page changed",                            // EVENT_PAGE_CHANGED
   "internal load",                           // EVENT_INTERNAL_LOAD
   "reorder"                                  // EVENT_REORDER
 };