diff --git a/src/backoff.rs b/src/backoff.rs
index 09412b05..afec84f2 100644
--- a/src/backoff.rs
+++ b/src/backoff.rs
@@ -85,9 +85,9 @@ impl Backoff {
     /// Perform an async operation that retries with a backoff
     pub async fn backy_offy<F, F1, B, C>(&mut self, request_name: &str, do_stuff: F) -> B
     where
-        F: Fn() -> F1,
-        F1: std::future::Future<Output = ControlFlow<B, C>>,
-        C: core::fmt::Display,
+        F: (Fn() -> F1) + Send + Sync,
+        F1: std::future::Future<Output = ControlFlow<B, C>> + Send,
+        C: core::fmt::Display + Send,
     {
         loop {
             let e = match do_stuff().await {
diff --git a/src/connection.rs b/src/connection.rs
index f7bc4721..2cc7f7b7 100644
--- a/src/connection.rs
+++ b/src/connection.rs
@@ -181,8 +181,8 @@ impl Connect for MessengerTransport {
 }
 
 #[async_trait]
-trait ArbitraryBrokerCache {
-    type C: Connect;
+trait ArbitraryBrokerCache: Send + Sync {
+    type C: Connect + Send + Sync;
 
     async fn get(&self) -> Result<Arc<Self::C>>;
 
@@ -282,7 +282,7 @@ mod tests {
     use crate::protocol::api_key::ApiKey;
     use std::sync::atomic::{AtomicBool, Ordering};
 
-    struct FakeBroker(Box<dyn Fn() -> Result<MetadataResponse, RequestError> + Sync>);
+    struct FakeBroker(Box<dyn Fn() -> Result<MetadataResponse, RequestError> + Send + Sync>);
 
     impl FakeBroker {
         fn success() -> Self {