diff --git a/pino.d.ts b/pino.d.ts
index 930c18c04..1227dcfcd 100644
--- a/pino.d.ts
+++ b/pino.d.ts
@@ -123,7 +123,7 @@ export interface LoggerExtras<Options = LoggerOptions> extends EventEmitter {
     /**
      * Flushes the content of the buffer when using pino.destination({ sync: false }).
      */
-    flush(): () => void;
+    flush(): void;
 }
 
 
diff --git a/test/syncfalse.test.js b/test/syncfalse.test.js
index cf169882e..b118ed9da 100644
--- a/test/syncfalse.test.js
+++ b/test/syncfalse.test.js
@@ -112,7 +112,7 @@ test('sync false with child', async ({ equal, teardown }) => {
   })
 })
 
-test('flush does nothing with sync true (default)', async () => {
+test('flush does nothing with sync true (default)', async ({ equal }) => {
   const instance = require('..')()
-  instance.flush()
+  equal(instance.flush(), undefined)
 })
diff --git a/test/transport/syncfalse.test.js b/test/transport/syncfalse.test.js
index 42ada5a6f..81111b532 100644
--- a/test/transport/syncfalse.test.js
+++ b/test/transport/syncfalse.test.js
@@ -10,7 +10,7 @@ const { watchFileCreated, file } = require('../helper')
 const { pid } = process
 const hostname = os.hostname()
 
-test('thread-stream async flush', async ({ same }) => {
+test('thread-stream async flush', async ({ equal, same }) => {
   const destination = file()
   const transport = pino.transport({
     target: join(__dirname, '..', 'fixtures', 'to-file-transport.js'),
@@ -18,7 +18,9 @@ test('thread-stream async flush', async ({ same }) => {
   })
   const instance = pino(transport)
   instance.info('hello')
-  instance.flush()
+
+  equal(instance.flush(), undefined)
+
   await watchFileCreated(destination)
   const result = JSON.parse(await readFile(destination))
   delete result.time
diff --git a/test/types/pino.test-d.ts b/test/types/pino.test-d.ts
index 6ae04f542..9e4786de6 100644
--- a/test/types/pino.test-d.ts
+++ b/test/types/pino.test-d.ts
@@ -111,6 +111,7 @@ pino({ base: null });
 // @ts-expect-error
 if ("pino" in log) console.log(`pino version: ${log.pino}`);
 
+expectType<void>(log.flush());
 log.child({ a: "property" }).info("hello child!");
 log.level = "error";
 log.info("nope");