diff --git a/iroh/examples/sync.rs b/iroh/examples/sync.rs
index 474ab699f2..f7bbe356a8 100644
--- a/iroh/examples/sync.rs
+++ b/iroh/examples/sync.rs
@@ -7,7 +7,10 @@
 //! `cargo run --bin derper -- --dev`
 //! and then set the `-d http://localhost:3340` flag on this example.
 
-use std::{collections::HashSet, fmt, net::SocketAddr, path::PathBuf, str::FromStr, sync::Arc};
+use std::{
+    collections::HashSet, fmt, net::SocketAddr, path::PathBuf, str::FromStr, sync::Arc,
+    time::Instant,
+};
 
 use anyhow::{anyhow, bail};
 use clap::{CommandFactory, FromArgMatches, Parser};
@@ -35,6 +38,7 @@ use serde::{Deserialize, Serialize};
 use tokio::{
     io::AsyncWriteExt,
     sync::{mpsc, oneshot},
+    task::JoinHandle,
 };
 use tracing::warn;
 use tracing_subscriber::{EnvFilter, Registry};
@@ -360,56 +364,58 @@ async fn handle_command(
                 "> Hammering with prefix \"{prefix}\" for {threads} x {count} messages of size {size} bytes in {mode} mode",
                 mode = format!("{mode:?}").to_lowercase()
             );
-            let start = std::time::Instant::now();
-            let mut handles = Vec::new();
+            let start = Instant::now();
+            let mut handles: Vec<JoinHandle<anyhow::Result<()>>> = Vec::new();
             match mode {
                 HammerMode::Set => {
                     let mut bytes = vec![0; size];
+                    // TODO: Add a flag to fill content differently per entry to be able to
+                    // test downloading too
                     bytes.fill(97);
                     for t in 0..threads {
-                        let p = prefix.clone();
-                        let t_doc = doc.clone();
-                        let b = bytes.clone();
-                        let h = tokio::spawn(async move {
+                        let prefix = prefix.clone();
+                        let doc = doc.clone();
+                        let bytes = bytes.clone();
+                        let handle = tokio::spawn(async move {
                             for i in 0..count {
-                                let value = String::from_utf8(b.clone()).unwrap();
-                                let key = format!("{}/{}/{}", p, t, i);
-                                t_doc
-                                    .insert_bytes(key, value.into_bytes().into())
-                                    .await
-                                    .unwrap();
+                                let value = String::from_utf8(bytes.clone()).unwrap();
+                                let key = format!("{}/{}/{}", prefix, t, i);
+                                doc.insert_bytes(key, value.into_bytes().into()).await?;
                             }
+                            Ok(())
                         });
-                        handles.push(h);
+                        handles.push(handle);
                     }
                 }
                 HammerMode::Get => {
                     for t in 0..threads {
-                        let p = prefix.clone();
-                        let t_doc = doc.clone();
-                        let h = tokio::spawn(async move {
+                        let prefix = prefix.clone();
+                        let doc = doc.clone();
+                        let handle = tokio::spawn(async move {
                             for i in 0..count {
-                                let key = format!("{}/{}/{}", p, t, i);
-                                let entries = t_doc.replica().all_for_key(key.as_bytes());
+                                let key = format!("{}/{}/{}", prefix, t, i);
+                                let entries = doc.replica().all_for_key(key.as_bytes());
                                 for (_id, entry) in entries {
-                                    let _content = fmt_content(&t_doc, &entry).await;
+                                    let _content = fmt_content(&doc, &entry).await;
                                 }
                             }
+                            Ok(())
                         });
-                        handles.push(h);
+                        handles.push(handle);
                     }
                 }
             }
 
-            let _result = futures::future::join_all(handles).await;
+            for result in futures::future::join_all(handles).await {
+                // Check that no errors ocurred
+                result??;
+            }
 
             let diff = start.elapsed().as_secs_f64();
             let total_count = threads as u64 * count as u64;
             println!(
-                "> Hammering done in {:.2}s for {} messages with total of {}",
-                diff,
-                total_count,
-                HumanBytes(total_count * size as u64),
+                "> Hammering done in {diff:.2}s for {total_count} messages with total of {size}",
+                size = HumanBytes(total_count * size as u64),
             );
         }
         Cmd::Exit => {}