diff --git a/aio/content/examples/practical-observable-usage/src/backoff.ts b/aio/content/examples/practical-observable-usage/src/backoff.ts
index 97b53845f1..e9e88e7cb2 100644
--- a/aio/content/examples/practical-observable-usage/src/backoff.ts
+++ b/aio/content/examples/practical-observable-usage/src/backoff.ts
@@ -5,10 +5,9 @@ import { retryWhen, map, mergeMap } from 'rxjs/operators';
 
 function backoff(maxTries, ms) {
  return pipe(
-   retryWhen(attempts => range(1, maxTries)
+   retryWhen(attempts => zip(range(1, maxTries), attempts)
      .pipe(
-       zip(attempts, (i) => i),
-       map(i => i * i),
+       map(([i]) => i * i),
        mergeMap(i =>  timer(i * ms))
      )
    )