diff --git a/mailnews/compose/src/nsMsgSend.cpp b/mailnews/compose/src/nsMsgSend.cpp
--- a/mailnews/compose/src/nsMsgSend.cpp
+++ b/mailnews/compose/src/nsMsgSend.cpp
@@ -2252,17 +2252,17 @@ nsMsgComposeAndSend::AddCompFieldLocalAt
             nsAutoString proposedName;
             attachment->GetName(proposedName);
             msg_pick_real_name(&m_attachments[newLoc], proposedName.get(), mCompFields->GetCharacterSet());
           }
 
           // Now, most importantly, we need to figure out what the content type is for
           // this attachment...If we can't, then just make it application/octet-stream
 
-  #ifdef MAC_OSX
+  #ifdef XP_MACOSX
           //Mac always need to snarf the file to figure out how to send it, maybe we need to use apple double...
           //  unless caller has already set the content type, in which case, trust them.
           PRBool mustSnarfAttachment = PR_TRUE;
   #else
           PRBool mustSnarfAttachment = PR_FALSE;
   #endif
           PR_FREEIF(m_attachments[newLoc].m_type);
           attachment->GetContentType(&m_attachments[newLoc].m_type);