diff --git a/modules/ui/tools.js b/modules/ui/tools.js
index be1b2f47..2fe930ac 100644
--- a/modules/ui/tools.js
+++ b/modules/ui/tools.js
@@ -703,9 +703,9 @@ function addMarkerOnClick() {
   const point = d3.mouse(this);
   const x = rn(point[0], 2);
   const y = rn(point[1], 2);
-  const i = last(markers).i + 1;
+  const i = markers.length ? last(markers).i + 1 : 0;
 
-  const isMarkerSelected = elSelected?.node()?.parentElement?.id === "markers";
+  const isMarkerSelected = markers.length && elSelected?.node()?.parentElement?.id === "markers";
   const selectedMarker = isMarkerSelected ? markers.find(marker => marker.i === +elSelected.attr("id").slice(6)) : null;
   const baseMarker = selectedMarker || {icon: "❓"};
   const marker = {...baseMarker, i, x, y};