diff --git a/src/async.rs b/src/async.rs
index 8edba37..d28562a 100644
--- a/src/async.rs
+++ b/src/async.rs
@@ -41,6 +41,7 @@ pub struct AsyncClient<S = DefaultSleeper> {
     /// Number of times to retry a request
     max_retries: usize,
 
+    /// Marker for the type of sleeper used
     marker: PhantomData<S>,
 }