diff --git a/tokio/src/io/util/mem.rs b/tokio/src/io/util/mem.rs
index 1510db34587..4019db56ff4 100644
--- a/tokio/src/io/util/mem.rs
+++ b/tokio/src/io/util/mem.rs
@@ -245,7 +245,7 @@ impl AsyncRead for Pipe {
 
     cfg_not_coop! {
         fn poll_read(
-            mut self: Pin<&mut Self>,
+            self: Pin<&mut Self>,
             cx: &mut task::Context<'_>,
             buf: &mut ReadBuf<'_>,
         ) -> Poll<std::io::Result<()>> {
@@ -273,7 +273,7 @@ impl AsyncWrite for Pipe {
 
     cfg_not_coop! {
         fn poll_write(
-            mut self: Pin<&mut Self>,
+            self: Pin<&mut Self>,
             cx: &mut task::Context<'_>,
             buf: &[u8],
         ) -> Poll<std::io::Result<usize>> {
diff --git a/tokio/tests/io_mem_stream.rs b/tokio/tests/io_mem_stream.rs
index 4b5e7b7746f..a2c2dadfc90 100644
--- a/tokio/tests/io_mem_stream.rs
+++ b/tokio/tests/io_mem_stream.rs
@@ -111,9 +111,9 @@ async fn duplex_is_cooperative() {
         _ = async {
             loop {
                 let buf = [3u8; 4096];
-                let _ = tx.write_all(&buf).await;
+                tx.write_all(&buf).await.unwrap();
                 let mut buf = [0u8; 4096];
-                let _ = rx.read(&mut buf).await;
+                rx.read(&mut buf).await.unwrap();
             }
         } => {},
         _ = tokio::task::yield_now() => {}