diff --git a/macrovision.js b/macrovision.js
index 2b045737..db975a46 100644
--- a/macrovision.js
+++ b/macrovision.js
@@ -980,7 +980,17 @@ function updateSizes(dirtyOnly = false) {
     drawRulers();
 }
 
+function cleanRulers() {
+    rulers = rulers.filter(ruler => {
+        if (!ruler.entityKey) {
+            return true;
+        } else {
+            return entities[ruler.entityKey] !== undefined;
+        }
+    });
+}
 function drawRulers() {
+    cleanRulers();
     const canvas = document.querySelector("#rulers");
 
     /** @type {CanvasRenderingContext2D} */