diff --git a/coordinator/src/tests/mod.rs b/coordinator/src/tests/mod.rs
index 6aaa907a..9a01e122 100644
--- a/coordinator/src/tests/mod.rs
+++ b/coordinator/src/tests/mod.rs
@@ -1,7 +1,7 @@
 use core::fmt::Debug;
 use std::{
   sync::Arc,
-  collections::{VecDeque, HashMap},
+  collections::{VecDeque, HashSet, HashMap},
 };
 
 use serai_client::primitives::NetworkId;
@@ -45,11 +45,11 @@ impl Processors for MemProcessors {
 
 #[allow(clippy::type_complexity)]
 #[derive(Clone, Debug)]
-pub struct LocalP2p(usize, pub Arc<RwLock<Vec<VecDeque<(usize, Vec<u8>)>>>>);
+pub struct LocalP2p(usize, pub Arc<RwLock<(HashSet<Vec<u8>>, Vec<VecDeque<(usize, Vec<u8>)>>)>>);
 
 impl LocalP2p {
   pub fn new(validators: usize) -> Vec<LocalP2p> {
-    let shared = Arc::new(RwLock::new(vec![VecDeque::new(); validators]));
+    let shared = Arc::new(RwLock::new((HashSet::new(), vec![VecDeque::new(); validators])));
     let mut res = vec![];
     for i in 0 .. validators {
       res.push(LocalP2p(i, shared.clone()));
@@ -63,11 +63,22 @@ impl P2p for LocalP2p {
   type Id = usize;
 
   async fn send_raw(&self, to: Self::Id, msg: Vec<u8>) {
-    self.1.write().await[to].push_back((self.0, msg));
+    self.1.write().await.1[to].push_back((self.0, msg));
   }
 
   async fn broadcast_raw(&self, msg: Vec<u8>) {
-    for (i, msg_queue) in self.1.write().await.iter_mut().enumerate() {
+    // Content-based deduplication
+    let mut lock = self.1.write().await;
+    {
+      let already_sent = &mut lock.0;
+      if already_sent.contains(&msg) {
+        return;
+      }
+      already_sent.insert(msg.clone());
+    }
+    let queues = &mut lock.1;
+
+    for (i, msg_queue) in queues.iter_mut().enumerate() {
       if i == self.0 {
         continue;
       }
@@ -78,7 +89,7 @@ impl P2p for LocalP2p {
   async fn receive_raw(&self) -> (Self::Id, Vec<u8>) {
     // This is a cursed way to implement an async read from a Vec
     loop {
-      if let Some(res) = self.1.write().await[self.0].pop_front() {
+      if let Some(res) = self.1.write().await.1[self.0].pop_front() {
         return res;
       }
       tokio::time::sleep(std::time::Duration::from_millis(100)).await;
diff --git a/coordinator/src/tests/tributary/sync.rs b/coordinator/src/tests/tributary/sync.rs
index 3dfc3757..bf13a735 100644
--- a/coordinator/src/tests/tributary/sync.rs
+++ b/coordinator/src/tests/tributary/sync.rs
@@ -70,7 +70,7 @@ async fn sync_test() {
 
   // Now that we've confirmed the other tributaries formed a net without issue, drop the syncer's
   // pending P2P messages
-  syncer_p2p.1.write().await.last_mut().unwrap().clear();
+  syncer_p2p.1.write().await.1.last_mut().unwrap().clear();
 
   // Have it join the net
   let syncer_key = Ristretto::generator() * *syncer_key;