diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index 7bc4c7e0..c0368075 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -8,6 +8,7 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
+  RUSTFLAGS: '-Dwarnings' # Never tolerate warnings.
 
 jobs:
   build:
diff --git a/test-harness/src/lib.rs b/test-harness/src/lib.rs
index 4c4820cc..188d4791 100644
--- a/test-harness/src/lib.rs
+++ b/test-harness/src/lib.rs
@@ -451,6 +451,7 @@ impl Arbitrary for TestConfig {
         c.set_window_update_mode(if bool::arbitrary(g) {
             WindowUpdateMode::OnRead
         } else {
+            #[allow(deprecated)]
             WindowUpdateMode::OnReceive
         });
         c.set_read_after_close(Arbitrary::arbitrary(g));
diff --git a/yamux/src/connection/cleanup.rs b/yamux/src/connection/cleanup.rs
index b4dfa816..87c6d0ca 100644
--- a/yamux/src/connection/cleanup.rs
+++ b/yamux/src/connection/cleanup.rs
@@ -33,7 +33,7 @@ impl Future for Cleanup {
     type Output = ConnectionError;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let mut this = self.get_mut();
+        let this = self.get_mut();
 
         loop {
             match this.state {
diff --git a/yamux/src/connection/closing.rs b/yamux/src/connection/closing.rs
index d503941f..b02c465e 100644
--- a/yamux/src/connection/closing.rs
+++ b/yamux/src/connection/closing.rs
@@ -45,7 +45,7 @@ where
     type Output = Result<()>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let mut this = self.get_mut();
+        let this = self.get_mut();
 
         loop {
             match this.state {
diff --git a/yamux/src/frame/io.rs b/yamux/src/frame/io.rs
index 795d9f5c..43e03987 100644
--- a/yamux/src/frame/io.rs
+++ b/yamux/src/frame/io.rs
@@ -171,7 +171,7 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Stream for Io<T> {
     type Item = Result<Frame<()>, FrameDecodeError>;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        let mut this = &mut *self;
+        let this = &mut *self;
         loop {
             log::trace!("{}: read: {:?}", this.id, this.read_state);
             match this.read_state {