diff --git a/lib/log4js.js b/lib/log4js.js
index 323ce11..641adeb 100644
--- a/lib/log4js.js
+++ b/lib/log4js.js
@@ -111,7 +111,10 @@ function shutdown(cb) {
   );
   if (shutdownFunctions === 0) {
     debug('No appenders with shutdown functions found.');
-    return cb !== undefined && cb();
+    if (cb) {
+      cb(undefined);
+    }
+    return null;
   }
 
   let completed = 0;
diff --git a/types/log4js.d.ts b/types/log4js.d.ts
index 7606fcb..cd4d8ae 100644
--- a/types/log4js.d.ts
+++ b/types/log4js.d.ts
@@ -17,7 +17,7 @@ export interface Log4js {
     options: { format?: Format; level?: string; nolog?: any }
   ): any; // express.Handler;
   levels: Levels;
-  shutdown(cb: (error: Error) => void): void | null;
+  shutdown(cb?: (error: Error | undefined) => void): null;
 }
 
 export function getLogger(category?: string): Logger;
@@ -45,7 +45,7 @@ export function recording(): Recording;
 
 export const levels: Levels;
 
-export function shutdown(cb?: (error: Error) => void): void | null;
+export function shutdown(cb?: (error: Error | undefined) => void): null;
 
 export interface BasicLayout {
   type: 'basic';