diff --git a/mozilla/content/html/document/src/nsHTMLContentSink.cpp b/mozilla/content/html/document/src/nsHTMLContentSink.cpp
index 388154ac8d1..a23af3ad1fc 100644
--- a/mozilla/content/html/document/src/nsHTMLContentSink.cpp
+++ b/mozilla/content/html/document/src/nsHTMLContentSink.cpp
@@ -826,15 +826,22 @@ NS_CreateHTMLElement(nsIHTMLContent** aResult, nsINodeInfo *aNodeInfo)
                   &rv);
 
   if (NS_SUCCEEDED(rv)) {
-    nsAutoString tag;
-    aNodeInfo->GetName(tag);
+    nsAutoString tmpName;
+    aNodeInfo->GetName(tmpName);
     // Find tag in tag table
     PRInt32 id; 
+    rv = parserService->HTMLStringTagToId(tmpName, &id);
+    if (eHTMLTag_userdefined == nsHTMLTag(id)) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
 
-    rv = parserService->HTMLStringTagToId(tag, &id);
+    // Create atom for tag and then create content object
+    nsAutoString tag;
+    rv = parserService->HTMLIdToStringTag(id, tag);
     nsCOMPtr<nsIAtom> atom(dont_AddRef(NS_NewAtom(tag.GetUnicode())));
     nsCOMPtr<nsINodeInfo> newName;
     aNodeInfo->NameChanged(atom, *getter_AddRefs(newName));
+
     rv = MakeContentObject(nsHTMLTag(id), newName, nsnull, nsnull, aResult);
   }
 
diff --git a/mozilla/layout/html/document/src/nsHTMLContentSink.cpp b/mozilla/layout/html/document/src/nsHTMLContentSink.cpp
index 388154ac8d1..a23af3ad1fc 100644
--- a/mozilla/layout/html/document/src/nsHTMLContentSink.cpp
+++ b/mozilla/layout/html/document/src/nsHTMLContentSink.cpp
@@ -826,15 +826,22 @@ NS_CreateHTMLElement(nsIHTMLContent** aResult, nsINodeInfo *aNodeInfo)
                   &rv);
 
   if (NS_SUCCEEDED(rv)) {
-    nsAutoString tag;
-    aNodeInfo->GetName(tag);
+    nsAutoString tmpName;
+    aNodeInfo->GetName(tmpName);
     // Find tag in tag table
     PRInt32 id; 
+    rv = parserService->HTMLStringTagToId(tmpName, &id);
+    if (eHTMLTag_userdefined == nsHTMLTag(id)) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
 
-    rv = parserService->HTMLStringTagToId(tag, &id);
+    // Create atom for tag and then create content object
+    nsAutoString tag;
+    rv = parserService->HTMLIdToStringTag(id, tag);
     nsCOMPtr<nsIAtom> atom(dont_AddRef(NS_NewAtom(tag.GetUnicode())));
     nsCOMPtr<nsINodeInfo> newName;
     aNodeInfo->NameChanged(atom, *getter_AddRefs(newName));
+
     rv = MakeContentObject(nsHTMLTag(id), newName, nsnull, nsnull, aResult);
   }