diff --git a/src/volume.ts b/src/volume.ts
index f2e4bcc1..2fce84b2 100644
--- a/src/volume.ts
+++ b/src/volume.ts
@@ -2136,7 +2136,7 @@ export class StatWatcher extends EventEmitter {
   interval: number;
   timeoutRef?;
   setTimeout: TSetTimeout;
-  prev: Stats = null;
+  prev: Stats;
 
   constructor(vol: Volume) {
     super();