diff --git a/app/assets/stylesheets/leaflet.zoom.css.scss b/app/assets/stylesheets/leaflet.zoom.css.scss
index a3ab049de..22640643a 100644
--- a/app/assets/stylesheets/leaflet.zoom.css.scss
+++ b/app/assets/stylesheets/leaflet.zoom.css.scss
@@ -11,7 +11,7 @@
 
 .leaflet-control-zoomslider-in,
 .leaflet-control-zoomslider-out {
-  text-indent: -9999;
+  text-indent: -9999px;
   outline-style: none;
 }