diff --git a/mozilla/mailnews/base/util/nsMsgProtocol.h b/mozilla/mailnews/base/util/nsMsgProtocol.h
index 3b5a46b9a57..eac555977c8 100644
--- a/mozilla/mailnews/base/util/nsMsgProtocol.h
+++ b/mozilla/mailnews/base/util/nsMsgProtocol.h
@@ -26,6 +26,7 @@
 #include "nsIChannel.h"
 #include "nsIURL.h"
 #include "nsILoadGroup.h"
+#include "nsIPrincipal.h"
 #include "nsCOMPtr.h"
 
 // This is a helper class used to encapsulate code shared between all of the