diff --git a/mozilla/mailnews/mime/src/mimemoz2.cpp b/mozilla/mailnews/mime/src/mimemoz2.cpp
index fb56e8baec9..eb3377e7645 100644
--- a/mozilla/mailnews/mime/src/mimemoz2.cpp
+++ b/mozilla/mailnews/mime/src/mimemoz2.cpp
@@ -448,7 +448,7 @@ GenerateAttachmentData(MimeObject *object, const char *aMessageURL, MimeDisplayO
   }
   nsCString urlString(urlSpec);
 
-  if (tmp->real_name)
+  if (tmp->real_name && !tmp->isExternalAttachment)
   {
     urlString.Append("&filename=");
     urlString.Append(tmp->real_name);