diff --git a/mapper/src/App.js b/mapper/src/App.js
index 2174ac5..755e47a 100644
--- a/mapper/src/App.js
+++ b/mapper/src/App.js
@@ -436,8 +436,8 @@ function Menu({data, duration, setDuration, end, setEnd, slider, setSlider, subm
 		const endUnix = moment(longestSegment.end).unix();
 		const endOfWindowUnix = end.unix();
 
-		const newSliderStart = Math.round((startUnix - endOfWindowUnix) / duration.secs + duration.num);
-		const newSliderEnd = Math.round((endUnix - endOfWindowUnix) / duration.secs + duration.num);
+		const newSliderStart = Math.floor((startUnix - endOfWindowUnix) / duration.secs + duration.num);
+		const newSliderEnd = Math.ceil((endUnix - endOfWindowUnix) / duration.secs + duration.num);
 
 		const clampedStart = Math.max(0, newSliderStart);
 		const clampedEnd = Math.min(duration.num, newSliderEnd);