diff --git a/tokio/src/sync/mpsc/bounded.rs b/tokio/src/sync/mpsc/bounded.rs
index a1e0a82d9..3cdba3dc2 100644
--- a/tokio/src/sync/mpsc/bounded.rs
+++ b/tokio/src/sync/mpsc/bounded.rs
@@ -1367,6 +1367,7 @@ impl<T> Sender<T> {
     /// towards RAII semantics, i.e. if all `Sender` instances of the
     /// channel were dropped and only `WeakSender` instances remain,
     /// the channel is closed.
+    #[must_use = "Downgrade creates a WeakSender without destroying the original non-weak sender."]
     pub fn downgrade(&self) -> WeakSender<T> {
         WeakSender {
             chan: self.chan.downgrade(),
diff --git a/tokio/src/sync/mpsc/unbounded.rs b/tokio/src/sync/mpsc/unbounded.rs
index 7dff942ee..b87b07ba6 100644
--- a/tokio/src/sync/mpsc/unbounded.rs
+++ b/tokio/src/sync/mpsc/unbounded.rs
@@ -572,6 +572,7 @@ impl<T> UnboundedSender<T> {
     /// towards RAII semantics, i.e. if all `UnboundedSender` instances of the
     /// channel were dropped and only `WeakUnboundedSender` instances remain,
     /// the channel is closed.
+    #[must_use = "Downgrade creates a WeakSender without destroying the original non-weak sender."]
     pub fn downgrade(&self) -> WeakUnboundedSender<T> {
         WeakUnboundedSender {
             chan: self.chan.downgrade(),