diff --git a/mozilla/mailnews/imap/src/nsImapProtocol.h b/mozilla/mailnews/imap/src/nsImapProtocol.h
index ae722541df9..797e8b27a71 100644
--- a/mozilla/mailnews/imap/src/nsImapProtocol.h
+++ b/mozilla/mailnews/imap/src/nsImapProtocol.h
@@ -42,6 +42,7 @@
 #include "nsIThread.h"
 #include "nsIImapMockChannel.h"
 #include "nsILoadGroup.h"
+#include "nsIPrincipal.h"
 #include "nsCOMPtr.h"
 
 class nsIMAPMessagePartIDArray;