diff --git a/src/concurrency/lazy-thenable.spec.ts b/src/concurrency/lazy-thenable.spec.ts
index 41d6463..6d05f47 100644
--- a/src/concurrency/lazy-thenable.spec.ts
+++ b/src/concurrency/lazy-thenable.spec.ts
@@ -7,10 +7,13 @@ describe(lazyThenable, () => {
     const lazy1 = lazyThenable(async () => ++called);
 
     expect(called).toEqual(0);
+    expect(lazy1.executed).toBe(false);
 
     const converted = Promise.resolve(lazy1);
     expect(called).toEqual(0);
+    expect(lazy1.executed).toBe(false);
     await wait(0);
+    expect(lazy1.executed).toBe(true);
     expect(called).toEqual(1);
     expect(await converted).toEqual(1);
     expect(await lazy1).toEqual(1);
diff --git a/src/concurrency/lazy-thenable.ts b/src/concurrency/lazy-thenable.ts
index d1954ed..6e1912a 100644
--- a/src/concurrency/lazy-thenable.ts
+++ b/src/concurrency/lazy-thenable.ts
@@ -3,14 +3,18 @@
  * @param io
  * @return
  */
-export function lazyThenable<T>(io: () => T): PromiseLike<Awaited<T>> {
+export function lazyThenable<T>(io: () => T): LazyThenable<Awaited<T>> {
   let r: null | Promise<Awaited<T>> = null;
   return {
-    then<TResult1, TResult2 = never>(
-      onfulfilled?: ((value: Awaited<T>) => PromiseLike<TResult1> | TResult1) | undefined | null,
-      onrejected?: ((reason: any) => PromiseLike<TResult2> | TResult2) | undefined | null,
-    ): PromiseLike<TResult1 | TResult2> {
+    get executed(): boolean {
+      return r !== null;
+    },
+    then(onfulfilled, onrejected): PromiseLike<any> {
       return (r ??= Promise.resolve(io())).then(onfulfilled, onrejected);
     },
   };
 }
+
+interface LazyThenable<T> extends PromiseLike<T> {
+  get executed(): boolean;
+}