diff --git a/extensions/Lily/Assets.js b/extensions/Lily/Assets.js
index ad5e3aaebb..4bc3f19adf 100644
--- a/extensions/Lily/Assets.js
+++ b/extensions/Lily/Assets.js
@@ -11,6 +11,16 @@
   const runtime = vm.runtime;
   const Cast = Scratch.Cast;
 
+  const requireNonPackagedRuntime = (blockName) => {
+    if (vm.runtime.isPackaged) {
+      alert(
+        `To use the Asset Manager ${blockName} block, the creator of the packaged project must uncheck "Remove raw asset data after loading to save RAM" under advanced settings in the packager.`
+      );
+      return false;
+    }
+    return true;
+  };
+
   class Assets {
     getInfo() {
       return {
@@ -517,14 +527,18 @@
       const costume = target.sprite.costumes[costumeIndex];
       switch (attribute) {
         case "dataURI":
+          if (!requireNonPackagedRuntime("dataURI of costume")) return "";
           return costume.asset.encodeDataURI();
         case "index":
           return costumeIndex + 1;
         case "format":
+          if (!requireNonPackagedRuntime("format of costume")) return "";
           return costume.asset.assetType.runtimeFormat;
         case "header":
+          if (!requireNonPackagedRuntime("header of costume")) return "";
           return costume.asset.assetType.contentType;
         case "asset ID":
+          if (!requireNonPackagedRuntime("asset ID of costume")) return "";
           return costume.asset.assetId;
         default:
           return "";
@@ -541,14 +555,18 @@
       const sound = target.sprite.sounds[soundIndex];
       switch (attribute) {
         case "dataURI":
+          if (!requireNonPackagedRuntime("dataURI of sound")) return "";
           return sound.asset.encodeDataURI();
         case "index":
           return soundIndex + 1;
         case "format":
+          if (!requireNonPackagedRuntime("format of sound")) return "";
           return sound.asset.assetType.runtimeFormat;
         case "header":
+          if (!requireNonPackagedRuntime("header of sound")) return "";
           return sound.asset.assetType.contentType;
         case "asset ID":
+          if (!requireNonPackagedRuntime("asset ID of sound")) return "";
           return sound.asset.assetId;
         default:
           return "";