diff --git a/client/src/connection_cache.rs b/client/src/connection_cache.rs
index 045ef57ca5..ce1a8b022d 100644
--- a/client/src/connection_cache.rs
+++ b/client/src/connection_cache.rs
@@ -145,20 +145,20 @@ impl Default for ConnectionCache {
 }
 
 macro_rules! dispatch {
-    ($(#[$meta:meta])* $vis:vis fn $name:ident$(<$($t:ident: $cons:ident),*>)?(&self $(, $arg:ident: $ty:ty)*) $(-> $out:ty)?) => {
+    ($(#[$meta:meta])* $vis:vis fn $name:ident$(<$($t:ident: $cons:ident + ?Sized),*>)?(&self $(, $arg:ident: $ty:ty)*) $(-> $out:ty)?) => {
         #[inline]
         $(#[$meta])*
-        $vis fn $name$(<$($t: $cons),*>)?(&self $(, $arg:$ty)*) $(-> $out)? {
+        $vis fn $name$(<$($t: $cons + ?Sized),*>)?(&self $(, $arg:$ty)*) $(-> $out)? {
             match self {
                 Self::Quic(this) => this.$name($($arg, )*),
                 Self::Udp(this) => this.$name($($arg, )*),
             }
         }
     };
-    ($(#[$meta:meta])* $vis:vis fn $name:ident$(<$($t:ident: $cons:ident),*>)?(&mut self $(, $arg:ident: $ty:ty)*) $(-> $out:ty)?) => {
+    ($(#[$meta:meta])* $vis:vis fn $name:ident$(<$($t:ident: $cons:ident + ?Sized),*>)?(&mut self $(, $arg:ident: $ty:ty)*) $(-> $out:ty)?) => {
         #[inline]
         $(#[$meta])*
-        $vis fn $name$(<$($t: $cons),*>)?(&mut self $(, $arg:$ty)*) $(-> $out)? {
+        $vis fn $name$(<$($t: $cons + ?Sized),*>)?(&mut self $(, $arg:$ty)*) $(-> $out)? {
             match self {
                 Self::Quic(this) => this.$name($($arg, )*),
                 Self::Udp(this) => this.$name($($arg, )*),
diff --git a/client/src/nonblocking/tpu_client.rs b/client/src/nonblocking/tpu_client.rs
index fb0f87a755..21c7c55a04 100644
--- a/client/src/nonblocking/tpu_client.rs
+++ b/client/src/nonblocking/tpu_client.rs
@@ -120,7 +120,7 @@ where
         })
     }
 
-    pub async fn send_and_confirm_messages_with_spinner<T: Signers>(
+    pub async fn send_and_confirm_messages_with_spinner<T: Signers + ?Sized>(
         &self,
         messages: &[Message],
         signers: &T,
diff --git a/client/src/thin_client.rs b/client/src/thin_client.rs
index aed9537ea8..559b904c13 100644
--- a/client/src/thin_client.rs
+++ b/client/src/thin_client.rs
@@ -124,7 +124,7 @@ impl ThinClient {
         tries: usize
     ) -> TransportResult<Signature>);
 
-    dispatch!(pub fn send_and_confirm_transaction<T: Signers>(
+    dispatch!(pub fn send_and_confirm_transaction<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         transaction: &mut Transaction,
@@ -172,7 +172,7 @@ impl Client for ThinClient {
 }
 
 impl SyncClient for ThinClient {
-    dispatch!(fn send_and_confirm_message<T: Signers>(
+    dispatch!(fn send_and_confirm_message<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         message: Message
diff --git a/client/src/tpu_client.rs b/client/src/tpu_client.rs
index ab39b59c74..7d32381445 100644
--- a/client/src/tpu_client.rs
+++ b/client/src/tpu_client.rs
@@ -111,7 +111,7 @@ where
         })
     }
 
-    pub fn send_and_confirm_messages_with_spinner<T: Signers>(
+    pub fn send_and_confirm_messages_with_spinner<T: Signers + ?Sized>(
         &self,
         messages: &[Message],
         signers: &T,
diff --git a/runtime/src/bank_client.rs b/runtime/src/bank_client.rs
index c553ee86a7..e4681db8aa 100644
--- a/runtime/src/bank_client.rs
+++ b/runtime/src/bank_client.rs
@@ -51,7 +51,7 @@ impl AsyncClient for BankClient {
 }
 
 impl SyncClient for BankClient {
-    fn send_and_confirm_message<T: Signers>(
+    fn send_and_confirm_message<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         message: Message,
diff --git a/sdk/program/src/example_mocks.rs b/sdk/program/src/example_mocks.rs
index a551a6dc6f..fdada265b6 100644
--- a/sdk/program/src/example_mocks.rs
+++ b/sdk/program/src/example_mocks.rs
@@ -213,7 +213,7 @@ pub mod solana_sdk {
         }
 
         impl VersionedTransaction {
-            pub fn try_new<T: Signers>(
+            pub fn try_new<T: Signers + ?Sized>(
                 message: VersionedMessage,
                 _keypairs: &T,
             ) -> std::result::Result<Self, SignerError> {
@@ -230,7 +230,7 @@ pub mod solana_sdk {
         }
 
         impl Transaction {
-            pub fn new<T: Signers>(
+            pub fn new<T: Signers + ?Sized>(
                 _from_keypairs: &T,
                 _message: Message,
                 _recent_blockhash: Hash,
@@ -252,7 +252,7 @@ pub mod solana_sdk {
                 }
             }
 
-            pub fn new_signed_with_payer<T: Signers>(
+            pub fn new_signed_with_payer<T: Signers + ?Sized>(
                 instructions: &[Instruction],
                 payer: Option<&Pubkey>,
                 signing_keypairs: &T,
@@ -262,9 +262,9 @@ pub mod solana_sdk {
                 Self::new(signing_keypairs, message, recent_blockhash)
             }
 
-            pub fn sign<T: Signers>(&mut self, _keypairs: &T, _recent_blockhash: Hash) {}
+            pub fn sign<T: Signers + ?Sized>(&mut self, _keypairs: &T, _recent_blockhash: Hash) {}
 
-            pub fn try_sign<T: Signers>(
+            pub fn try_sign<T: Signers + ?Sized>(
                 &mut self,
                 _keypairs: &T,
                 _recent_blockhash: Hash,
diff --git a/sdk/src/client.rs b/sdk/src/client.rs
index c2f7f62d35..f9e435c81d 100644
--- a/sdk/src/client.rs
+++ b/sdk/src/client.rs
@@ -34,7 +34,7 @@ pub trait Client: SyncClient + AsyncClient {
 pub trait SyncClient {
     /// Create a transaction from the given message, and send it to the
     /// server, retrying as-needed.
-    fn send_and_confirm_message<T: Signers>(
+    fn send_and_confirm_message<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         message: Message,
@@ -204,7 +204,7 @@ pub trait AsyncClient {
 
     /// Create a transaction from the given message, and send it to the
     /// server, but don't wait for to see if the server accepted it.
-    fn async_send_message<T: Signers>(
+    fn async_send_message<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         message: Message,
diff --git a/sdk/src/transaction/mod.rs b/sdk/src/transaction/mod.rs
index e5eb9fdba5..f1c7e2ed58 100644
--- a/sdk/src/transaction/mod.rs
+++ b/sdk/src/transaction/mod.rs
@@ -346,7 +346,7 @@ impl Transaction {
     /// #
     /// # Ok::<(), anyhow::Error>(())
     /// ```
-    pub fn new<T: Signers>(
+    pub fn new<T: Signers + ?Sized>(
         from_keypairs: &T,
         message: Message,
         recent_blockhash: Hash,
@@ -501,7 +501,7 @@ impl Transaction {
     /// #
     /// # Ok::<(), anyhow::Error>(())
     /// ```
-    pub fn new_signed_with_payer<T: Signers>(
+    pub fn new_signed_with_payer<T: Signers + ?Sized>(
         instructions: &[Instruction],
         payer: Option<&Pubkey>,
         signing_keypairs: &T,
@@ -526,7 +526,7 @@ impl Transaction {
     ///
     /// Panics when signing fails. See [`Transaction::try_sign`] and for a full
     /// description of failure conditions.
-    pub fn new_with_compiled_instructions<T: Signers>(
+    pub fn new_with_compiled_instructions<T: Signers + ?Sized>(
         from_keypairs: &T,
         keys: &[Pubkey],
         recent_blockhash: Hash,
@@ -705,7 +705,7 @@ impl Transaction {
     /// #
     /// # Ok::<(), anyhow::Error>(())
     /// ```
-    pub fn sign<T: Signers>(&mut self, keypairs: &T, recent_blockhash: Hash) {
+    pub fn sign<T: Signers + ?Sized>(&mut self, keypairs: &T, recent_blockhash: Hash) {
         if let Err(e) = self.try_sign(keypairs, recent_blockhash) {
             panic!("Transaction::sign failed with error {e:?}");
         }
@@ -731,7 +731,7 @@ impl Transaction {
     /// handle the error. See the documentation for
     /// [`Transaction::try_partial_sign`] for a full description of failure
     /// conditions.
-    pub fn partial_sign<T: Signers>(&mut self, keypairs: &T, recent_blockhash: Hash) {
+    pub fn partial_sign<T: Signers + ?Sized>(&mut self, keypairs: &T, recent_blockhash: Hash) {
         if let Err(e) = self.try_partial_sign(keypairs, recent_blockhash) {
             panic!("Transaction::partial_sign failed with error {e:?}");
         }
@@ -750,7 +750,7 @@ impl Transaction {
     ///
     /// Panics if signing fails. Use [`Transaction::try_partial_sign_unchecked`]
     /// to handle the error.
-    pub fn partial_sign_unchecked<T: Signers>(
+    pub fn partial_sign_unchecked<T: Signers + ?Sized>(
         &mut self,
         keypairs: &T,
         positions: Vec<usize>,
@@ -843,7 +843,7 @@ impl Transaction {
     /// #
     /// # Ok::<(), anyhow::Error>(())
     /// ```
-    pub fn try_sign<T: Signers>(
+    pub fn try_sign<T: Signers + ?Sized>(
         &mut self,
         keypairs: &T,
         recent_blockhash: Hash,
@@ -906,7 +906,7 @@ impl Transaction {
     /// [`PresignerError::VerificationFailure`]: crate::signer::presigner::PresignerError::VerificationFailure
     /// [`solana-remote-wallet`]: https://docs.rs/solana-remote-wallet/latest/
     /// [`RemoteKeypair`]: https://docs.rs/solana-remote-wallet/latest/solana_remote_wallet/remote_keypair/struct.RemoteKeypair.html
-    pub fn try_partial_sign<T: Signers>(
+    pub fn try_partial_sign<T: Signers + ?Sized>(
         &mut self,
         keypairs: &T,
         recent_blockhash: Hash,
@@ -932,7 +932,7 @@ impl Transaction {
     /// # Errors
     ///
     /// Returns an error if signing fails.
-    pub fn try_partial_sign_unchecked<T: Signers>(
+    pub fn try_partial_sign_unchecked<T: Signers + ?Sized>(
         &mut self,
         keypairs: &T,
         positions: Vec<usize>,
@@ -1668,4 +1668,22 @@ mod tests {
             .unwrap_err();
         assert_eq!(err, SignerError::KeypairPubkeyMismatch);
     }
+
+    #[test]
+    fn test_unsized_signers() {
+        fn instructions_to_tx(
+            instructions: &[Instruction],
+            signers: Box<dyn Signers>,
+        ) -> Transaction {
+            let pubkeys = signers.pubkeys();
+            let first_signer = pubkeys.first().expect("should exist");
+            let message = Message::new(instructions, Some(first_signer));
+            Transaction::new(signers.as_ref(), message, Hash::default())
+        }
+
+        let signer: Box<dyn Signer> = Box::new(Keypair::new());
+        let tx = instructions_to_tx(&[], Box::new(vec![signer]));
+
+        assert!(tx.is_signed());
+    }
 }
diff --git a/sdk/src/transaction/versioned/mod.rs b/sdk/src/transaction/versioned/mod.rs
index fd749c3892..29e385e627 100644
--- a/sdk/src/transaction/versioned/mod.rs
+++ b/sdk/src/transaction/versioned/mod.rs
@@ -68,7 +68,7 @@ impl From<Transaction> for VersionedTransaction {
 impl VersionedTransaction {
     /// Signs a versioned message and if successful, returns a signed
     /// transaction.
-    pub fn try_new<T: Signers>(
+    pub fn try_new<T: Signers + ?Sized>(
         message: VersionedMessage,
         keypairs: &T,
     ) -> std::result::Result<Self, SignerError> {
diff --git a/thin-client/src/thin_client.rs b/thin-client/src/thin_client.rs
index c383ee0201..b1ae08fd7c 100644
--- a/thin-client/src/thin_client.rs
+++ b/thin-client/src/thin_client.rs
@@ -209,7 +209,7 @@ where
         self.send_and_confirm_transaction(&[keypair], transaction, tries, 0)
     }
 
-    pub fn send_and_confirm_transaction<T: Signers>(
+    pub fn send_and_confirm_transaction<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         transaction: &mut Transaction,
@@ -340,7 +340,7 @@ where
     M: ConnectionManager<ConnectionPool = P, NewConnectionConfig = C>,
     C: NewConnectionConfig,
 {
-    fn send_and_confirm_message<T: Signers>(
+    fn send_and_confirm_message<T: Signers + ?Sized>(
         &self,
         keypairs: &T,
         message: Message,
diff --git a/tpu-client/src/nonblocking/tpu_client.rs b/tpu-client/src/nonblocking/tpu_client.rs
index 8214dfa6fb..d23de87526 100644
--- a/tpu-client/src/nonblocking/tpu_client.rs
+++ b/tpu-client/src/nonblocking/tpu_client.rs
@@ -437,7 +437,7 @@ where
     }
 
     #[cfg(feature = "spinner")]
-    pub async fn send_and_confirm_messages_with_spinner<T: Signers>(
+    pub async fn send_and_confirm_messages_with_spinner<T: Signers + ?Sized>(
         &self,
         messages: &[Message],
         signers: &T,
diff --git a/tpu-client/src/tpu_client.rs b/tpu-client/src/tpu_client.rs
index f2d62c5d77..a620d0e0ce 100644
--- a/tpu-client/src/tpu_client.rs
+++ b/tpu-client/src/tpu_client.rs
@@ -158,7 +158,7 @@ where
     }
 
     #[cfg(feature = "spinner")]
-    pub fn send_and_confirm_messages_with_spinner<T: Signers>(
+    pub fn send_and_confirm_messages_with_spinner<T: Signers + ?Sized>(
         &self,
         messages: &[Message],
         signers: &T,