diff --git a/javascript/newsim.js b/javascript/newsim.js
index 76d2f0c..52af4a6 100644
--- a/javascript/newsim.js
+++ b/javascript/newsim.js
@@ -5,11 +5,11 @@ let backgroundImage;
 let worldScale;
 let LEFT = [-1,0];
 
-const entityTypes = {
+const entityTypes = Object.freeze({
     METERORITE_SMALL: "meteorite_small",
     METERORITE_LARGE: "meteorite_large",
     COMET: "comet",
-};
+});
 
 var Settings = {
     windowWrap: true,