diff --git a/include/libtorrent/alert.hpp b/include/libtorrent/alert.hpp
index b77fa0da0..0579f5183 100644
--- a/include/libtorrent/alert.hpp
+++ b/include/libtorrent/alert.hpp
@@ -146,7 +146,7 @@ namespace libtorrent {
 
 		alert const* wait_for_alert(time_duration max_wait);
 
-		void set_alert_mask(int m)
+		void set_alert_mask(boost::uint32_t m)
 		{
 			mutex::scoped_lock lock(m_mutex);
 			m_alert_mask = m;
@@ -167,7 +167,7 @@ namespace libtorrent {
 		std::deque<alert*> m_alerts;
 		mutable mutex m_mutex;
 //		event m_condition;
-		int m_alert_mask;
+		boost::uint32_t m_alert_mask;
 		size_t m_queue_size_limit;
 		boost::function<void(std::auto_ptr<alert>)> m_dispatch;
 		io_service& m_ios;
diff --git a/include/libtorrent/session.hpp b/include/libtorrent/session.hpp
index d056f104d..c20a00905 100644
--- a/include/libtorrent/session.hpp
+++ b/include/libtorrent/session.hpp
@@ -127,7 +127,7 @@ namespace libtorrent
 		session(fingerprint const& print = fingerprint("LT"
 			, LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
 			, int flags = start_default_features | add_default_plugins
-			, int alert_mask = alert::error_notification
+			, boost::uint32_t alert_mask = alert::error_notification
 			TORRENT_LOGPATH_ARG_DEFAULT)
 		{
 			TORRENT_CFG();
@@ -455,7 +455,7 @@ namespace libtorrent
 		TORRENT_DEPRECATED_PREFIX
 		size_t set_alert_queue_size_limit(size_t queue_size_limit_) TORRENT_DEPRECATED;
 #endif
-		void set_alert_mask(int m);
+		void set_alert_mask(boost::uint32_t m);
 
 		alert const* wait_for_alert(time_duration max_wait);
 		void set_alert_dispatch(boost::function<void(std::auto_ptr<alert>)> const& fun);
@@ -475,7 +475,7 @@ namespace libtorrent
 	private:
 
 		void init(std::pair<int, int> listen_range, char const* listen_interface
-			, fingerprint const& id, int flags, int alert_mask TORRENT_LOGPATH_ARG);
+			, fingerprint const& id, int flags, boost::uint32_t alert_mask TORRENT_LOGPATH_ARG);
 
 		// data shared between the main thread
 		// and the working thread
diff --git a/src/session.cpp b/src/session.cpp
index d670706d6..ce36a21b6 100644
--- a/src/session.cpp
+++ b/src/session.cpp
@@ -379,7 +379,7 @@ namespace libtorrent
 	void TORRENT_EXPORT TORRENT_CFG() {}
 
 	void session::init(std::pair<int, int> listen_range, char const* listen_interface
-		, fingerprint const& id, int flags, int alert_mask TORRENT_LOGPATH_ARG)
+		, fingerprint const& id, int flags, boost::uint32_t alert_mask TORRENT_LOGPATH_ARG)
 	{
 		m_impl.reset(new session_impl(listen_range, id, listen_interface TORRENT_LOGPATH));
 
@@ -1020,7 +1020,7 @@ namespace libtorrent
 		return m_impl->wait_for_alert(max_wait);
 	}
 
-	void session::set_alert_mask(int m)
+	void session::set_alert_mask(boost::uint32_t m)
 	{
 		TORRENT_ASYNC_CALL1(set_alert_mask, m);
 	}
diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index dd7bf7ee3..d7496c5eb 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -4935,7 +4935,7 @@ namespace aux {
 		return m_alerts.wait_for_alert(max_wait);
 	}
 
-	void session_impl::set_alert_mask(int m)
+	void session_impl::set_alert_mask(boost::uint32_t m)
 	{
 		m_alerts.set_alert_mask(m);
 	}