diff --git a/src/tardismachine.ts b/src/tardismachine.ts
index eeb15b0..8f8c871 100644
--- a/src/tardismachine.ts
+++ b/src/tardismachine.ts
@@ -11,7 +11,7 @@ const pkg = require('../package.json')
 export class TardisMachine {
   private readonly _httpServer: http.Server
   private readonly _wsServer: TemplatedApp
-  private _eventLoopTimerId: number | undefined = undefined
+  private _eventLoopTimerId: NodeJS.Timeout | undefined = undefined
 
   constructor(private readonly options: Options) {
     init({