diff --git a/quinn-proto/src/config.rs b/quinn-proto/src/config.rs
index c51557a33..6d53fd590 100644
--- a/quinn-proto/src/config.rs
+++ b/quinn-proto/src/config.rs
@@ -630,8 +630,8 @@ pub struct EndpointConfig {
 impl EndpointConfig {
     /// Create a default config with a particular `reset_key`
     pub fn new(reset_key: Arc<dyn HmacKey>) -> Self {
-        let cid_factory: fn() -> Box<dyn ConnectionIdGenerator> =
-            || Box::<HashedConnectionIdGenerator>::default();
+        let cid_factory =
+            || -> Box<dyn ConnectionIdGenerator> { Box::<HashedConnectionIdGenerator>::default() };
         Self {
             reset_key,
             max_udp_payload_size: (1500u32 - 28).into(), // Ethernet MTU minus IP + UDP headers
diff --git a/quinn-proto/src/packet.rs b/quinn-proto/src/packet.rs
index 3e5bf0fd0..be132a74f 100644
--- a/quinn-proto/src/packet.rs
+++ b/quinn-proto/src/packet.rs
@@ -32,7 +32,7 @@ impl PartialDecode {
     /// Begin decoding a QUIC packet from `bytes`, returning any trailing data not part of that packet
     pub fn new(
         bytes: BytesMut,
-        cid_parser: &impl ConnectionIdParser,
+        cid_parser: &(impl ConnectionIdParser + ?Sized),
         supported_versions: &[u32],
         grease_quic_bit: bool,
     ) -> Result<(Self, Option<BytesMut>), PacketDecodeError> {
@@ -564,7 +564,7 @@ impl ProtectedHeader {
     /// Decode a plain header from given buffer, with given [`ConnectionIdParser`].
     pub fn decode(
         buf: &mut io::Cursor<BytesMut>,
-        cid_parser: &impl ConnectionIdParser,
+        cid_parser: &(impl ConnectionIdParser + ?Sized),
         supported_versions: &[u32],
         grease_quic_bit: bool,
     ) -> Result<Self, PacketDecodeError> {
@@ -780,7 +780,7 @@ impl FixedLengthConnectionIdParser {
 }
 
 impl ConnectionIdParser for FixedLengthConnectionIdParser {
-    fn parse(&self, buffer: &mut impl Buf) -> Result<ConnectionId, PacketDecodeError> {
+    fn parse(&self, buffer: &mut dyn Buf) -> Result<ConnectionId, PacketDecodeError> {
         (buffer.remaining() >= self.expected_len)
             .then(|| ConnectionId::from_buf(buffer, self.expected_len))
             .ok_or(PacketDecodeError::InvalidHeader("packet too small"))
@@ -790,7 +790,7 @@ impl ConnectionIdParser for FixedLengthConnectionIdParser {
 /// Parse connection id in short header packet
 pub trait ConnectionIdParser {
     /// Parse a connection id from given buffer
-    fn parse(&self, buf: &mut impl Buf) -> Result<ConnectionId, PacketDecodeError>;
+    fn parse(&self, buf: &mut dyn Buf) -> Result<ConnectionId, PacketDecodeError>;
 }
 
 /// Long packet type including non-uniform cases
diff --git a/quinn-proto/src/shared.rs b/quinn-proto/src/shared.rs
index d4e5029c7..05ffe8caf 100644
--- a/quinn-proto/src/shared.rs
+++ b/quinn-proto/src/shared.rs
@@ -86,7 +86,7 @@ impl ConnectionId {
     /// Constructs cid by reading `len` bytes from a `Buf`
     ///
     /// Callers need to assure that `buf.remaining() >= len`
-    pub fn from_buf(buf: &mut impl Buf, len: usize) -> Self {
+    pub fn from_buf(buf: &mut (impl Buf + ?Sized), len: usize) -> Self {
         debug_assert!(len <= MAX_CID_SIZE);
         let mut res = Self {
             len: len as u8,