diff --git a/include/libtorrent/time.hpp b/include/libtorrent/time.hpp
index 7a2a6dfed..eb94cd879 100644
--- a/include/libtorrent/time.hpp
+++ b/include/libtorrent/time.hpp
@@ -35,6 +35,7 @@ POSSIBILITY OF SUCH DAMAGE.
 
 #include <ctime>
 #include <boost/version.hpp>
+#include "libtorrent/config.hpp"
 
 #ifndef _WIN32
 #include <unistd.h>
@@ -106,6 +107,7 @@ namespace libtorrent
 		time_duration& operator-=(time_duration const& c) { diff -= c.diff; return *this; }
 		time_duration& operator+=(time_duration const& c) { diff += c.diff; return *this; }
 		time_duration operator+(time_duration const& c) { return time_duration(diff + c.diff); }
+		time_duration operator-(time_duration const& c) { return time_duration(diff - c.diff); }
 		boost::int64_t diff;
 	};
 
diff --git a/src/torrent.cpp b/src/torrent.cpp
index 22ae75d27..aa8c12aab 100644
--- a/src/torrent.cpp
+++ b/src/torrent.cpp
@@ -153,8 +153,8 @@ namespace libtorrent
 #endif
 		, m_ses(ses)
 		, m_trackers(m_torrent_file->trackers())
-		, m_average_piece_time(0)
-		, m_piece_time_deviation(0)
+		, m_average_piece_time(seconds(0))
+		, m_piece_time_deviation(seconds(0))
 		, m_total_failed_bytes(0)
 		, m_total_redundant_bytes(0)
 		, m_padding(0)
@@ -2099,7 +2099,7 @@ namespace libtorrent
 				}
 				else
 				{
-					time_duration diff = time_duration(dl_time.diff - m_average_piece_time.diff);
+					time_duration diff = dl_time - m_average_piece_time;
 					if (m_piece_time_deviation == seconds(0)) m_piece_time_deviation = diff;
 					else m_piece_time_deviation = m_piece_time_deviation * 0.6f + diff * 0.4;
 
@@ -4973,7 +4973,7 @@ namespace libtorrent
 			, end(m_time_critical_pieces.end()); i != end; ++i)
 		{
 			if (i != m_time_critical_pieces.begin() && i->deadline > now
-				+ m_average_piece_time + 4 * m_piece_time_deviation)
+				+ m_average_piece_time + m_piece_time_deviation * 4)
 			{
 				// don't request pieces whose deadline is too far in the future
 				break;