diff --git a/src/ext/hx-compat.js b/src/ext/hx-compat.js
index 0f45a0e1..22fd9ad4 100644
--- a/src/ext/hx-compat.js
+++ b/src/ext/hx-compat.js
@@ -10,7 +10,7 @@
         }
     }
 
-    htmx.defineExtension('compat', {
+    htmx.registerExtension('compat', {
         init: (internalAPI) => {
             api = internalAPI;