diff --git a/appengine/blockly_compressed.js b/appengine/blockly_compressed.js
new file mode 100644
index 000000000..dc118dfbe
--- /dev/null
+++ b/appengine/blockly_compressed.js
@@ -0,0 +1,11 @@
+// Added November 2022 after discovering that a number of orgs were hot-linking
+// their Blockly applications to https://blockly-demo.appspot.com/
+// Delete this file in early 2024.
+var msg = 'Compiled Blockly files should be loaded from https://unpkg.com/blockly/\n' +
+    'For help, contact https://groups.google.com/g/blockly';
+console.log(msg);
+try {
+  alert(msg);
+} catch (_e) {
+  // Can't alert?  Probably node.js.
+}