diff --git a/core/filtermaps/map_renderer.go b/core/filtermaps/map_renderer.go
index 2adf4e13ce..6c67a096df 100644
--- a/core/filtermaps/map_renderer.go
+++ b/core/filtermaps/map_renderer.go
@@ -429,7 +429,9 @@ func (r *mapRenderer) writeFinishedMaps(pauseCb func() bool) error {
 		base := len(r.finishedMaps)
 		extra := 0
 		if newRange.maps.AfterLast() == r.finished.AfterLast() {
-			extra = int(oldRange.maps.AfterLast() - r.finished.AfterLast())
+			if oldRange.maps.AfterLast() > r.finished.AfterLast() {
+				extra = int(oldRange.maps.AfterLast() - r.finished.AfterLast())
+			}
 		}
 		capacity := base + extra