diff --git a/src/asynchronous/client.rs b/src/asynchronous/client.rs
index ed2ee3a8..2eb36e58 100644
--- a/src/asynchronous/client.rs
+++ b/src/asynchronous/client.rs
@@ -74,8 +74,9 @@ impl Client {
 
         let (tx, mut rx): (ResultSender, ResultReceiver) = mpsc::channel(100);
 
-        // TODO: check return.
-        self.streams.lock().unwrap().insert(stream_id, tx);
+        self.streams.lock().map(|mut x| {
+            x.insert(stream_id, tx);
+        }).map_err(|_| Error::Others("Failed to acquire lock on streams".to_string()))?;
 
         self.req_tx
             .send(msg)
@@ -136,8 +137,10 @@ impl Client {
         }
 
         let (tx, rx): (ResultSender, ResultReceiver) = mpsc::channel(100);
-        // TODO: check return
-        self.streams.lock().unwrap().insert(stream_id, tx);
+        self.streams.lock().map(|mut x| {
+            x.insert(stream_id, tx);
+        }).map_err(|_| Error::Others("Failed to acquire lock on streams".to_string()))?;
+
         self.req_tx
             .send(msg)
             .await