diff --git a/common/rfb/Timer.cxx b/common/rfb/Timer.cxx
index 4654d50c8d..fbc9bae95e 100644
--- a/common/rfb/Timer.cxx
+++ b/common/rfb/Timer.cxx
@@ -54,7 +54,10 @@ inline static timeval addMillis(timeval inTime, int millis) {
 }
 
 inline static int diffTimeMillis(timeval later, timeval earlier) {
-  return ((later.tv_sec - earlier.tv_sec) * 1000) + ((later.tv_usec - earlier.tv_usec + 999) / 1000);
+  long udiff;
+  udiff = ((later.tv_sec - earlier.tv_sec) * 1000000) +
+          (later.tv_usec - earlier.tv_usec);
+  return (udiff + 999) / 1000;
 }
 
 std::list<Timer*> Timer::pending;