diff --git a/src/util/emitter.ts b/src/util/emitter.ts
index 0fe74d4e..cb008f62 100644
--- a/src/util/emitter.ts
+++ b/src/util/emitter.ts
@@ -9,7 +9,7 @@ export class Emitter<T> {
     // callback will run at a time, assuming the event is
     // sent with "await send(...)" and not just "send(...)".
     _callbacks : Callback<T>[] = [];
-    changeKey : number = 0;  // this becomes a new random value with every update
+    changeKey : string = 'init';  // this becomes a new random value with every update
     constructor() {
     }
     subscribe(cb : Callback<T>) : Thunk {
@@ -20,7 +20,7 @@ export class Emitter<T> {
         };
     }
     async send(t : T) : Promise<void> {
-        this.changeKey = Math.random();
+        this.changeKey = '' + Math.random();
         for (let cb of this._callbacks) {
             let result = cb(t);
             if (result instanceof Promise) {