diff --git a/include/libtorrent/aux_/session_impl.hpp b/include/libtorrent/aux_/session_impl.hpp
index 99fb72d3e..26960e630 100644
--- a/include/libtorrent/aux_/session_impl.hpp
+++ b/include/libtorrent/aux_/session_impl.hpp
@@ -283,7 +283,7 @@ namespace libtorrent
 			void queue_check_torrent(boost::shared_ptr<torrent> const& t);
 			void dequeue_check_torrent(boost::shared_ptr<torrent> const& t);
 
-			void set_alert_mask(int m);
+			void set_alert_mask(boost::uint32_t m);
 			size_t set_alert_queue_size_limit(size_t queue_size_limit_);
 			std::auto_ptr<alert> pop_alert();
 			void pop_alerts(std::deque<alert*>* alerts);