diff --git a/src/handlers/isExtensible.ts b/src/handlers/isExtensible.ts
new file mode 100644
index 0000000..3ba174f
--- /dev/null
+++ b/src/handlers/isExtensible.ts
@@ -0,0 +1,22 @@
+import Nexo from "../types/Nexo.js";
+import { map } from "../utils/index.js";
+import ProxyHandlerEvent from "../events/ProxyHandlerEvent.js";
+
+const isExtensible = (mock: Nexo.Mock): boolean => {
+  const proxy = map.tracables.get(mock);
+  const data = map.proxies.get(proxy);
+
+  const scope = data.scope.deref();
+
+  const event = new ProxyHandlerEvent("isExtensible", proxy);
+
+  scope.emit(event.name, event);
+
+  if (event.defaultPrevented) {
+    return event.returnValue === true;
+  }
+
+  return true;
+};
+
+export default isExtensible;
diff --git a/src/types/Nexo.ts b/src/types/Nexo.ts
index a56b6ee..c2ab34f 100644
--- a/src/types/Nexo.ts
+++ b/src/types/Nexo.ts
@@ -37,7 +37,8 @@ declare namespace Nexo {
       | "defineProperty"
       | "apply"
       | "construct"
-      | "getPrototypeOf";
+      | "getPrototypeOf"
+      | "isExtensible";
   }
 }