diff --git a/node/actors/executor/src/attestation.rs b/node/actors/executor/src/attestation.rs
index d7d21918..3a5146fc 100644
--- a/node/actors/executor/src/attestation.rs
+++ b/node/actors/executor/src/attestation.rs
@@ -46,6 +46,8 @@ impl AttesterRunner {
             return Ok(());
         }
 
+        let genesis = self.block_store.genesis().hash();
+
         // Find the initial range of batches that we want to (re)sign after a (re)start.
         let last_batch_number = self
             .batch_store
@@ -79,7 +81,7 @@ impl AttesterRunner {
 
             // We only have to publish a vote once; future peers can pull it from the register.
             self.publisher
-                .publish(attesters, &self.attester.key, batch)
+                .publish(attesters, &genesis, &self.attester.key, batch)
                 .await
                 .context("publish")?;
 
diff --git a/node/actors/network/src/gossip/batch_votes.rs b/node/actors/network/src/gossip/batch_votes.rs
index 1a9f0f3c..1f5ad613 100644
--- a/node/actors/network/src/gossip/batch_votes.rs
+++ b/node/actors/network/src/gossip/batch_votes.rs
@@ -78,6 +78,7 @@ impl BatchVotes {
     pub(super) fn update(
         &mut self,
         attesters: &attester::Committee,
+        genesis: &attester::GenesisHash,
         data: &[Arc<attester::Signed<attester::Batch>>],
     ) -> anyhow::Result<BatchUpdateStats> {
         let mut stats = BatchUpdateStats::default();
@@ -92,6 +93,14 @@ impl BatchVotes {
             }
             done.insert(d.key.clone());
 
+            // Disallow votes from different genesis. It might indicate a reorg,
+            // in which case either this node or the remote peer has to be restarted.
+            anyhow::ensure!(
+                d.msg.genesis == *genesis,
+                "vote for batch with different genesis hash: {:?}",
+                d.msg.genesis
+            );
+
             if d.msg.number < self.min_batch_number {
                 continue;
             }
@@ -129,6 +138,7 @@ impl BatchVotes {
     pub(super) fn find_quorums(
         &self,
         attesters: &attester::Committee,
+        genesis: &attester::GenesisHash,
         skip: impl Fn(attester::BatchNumber) -> bool,
     ) -> Vec<attester::BatchQC> {
         let threshold = attesters.threshold();
@@ -153,6 +163,8 @@ impl BatchVotes {
                             message: attester::Batch {
                                 number: *number,
                                 hash: *hash,
+                                // This was checked during insertion; we could look up the first in `votes`
+                                genesis: *genesis,
                             },
                             signatures: sigs,
                         }
@@ -229,11 +241,12 @@ impl BatchVotesWatch {
     pub(crate) async fn update(
         &self,
         attesters: &attester::Committee,
+        genesis: &attester::GenesisHash,
         data: &[Arc<attester::Signed<attester::Batch>>],
     ) -> anyhow::Result<()> {
         let this = self.0.lock().await;
         let mut votes = this.borrow().clone();
-        let stats = votes.update(attesters, data)?;
+        let stats = votes.update(attesters, genesis, data)?;
 
         if let Some(last_added) = stats.last_added {
             this.send_replace(votes);
@@ -287,6 +300,7 @@ impl BatchVotesPublisher {
     pub async fn publish(
         &self,
         attesters: &attester::Committee,
+        genesis: &attester::GenesisHash,
         attester: &attester::SecretKey,
         batch: attester::Batch,
     ) -> anyhow::Result<()> {
@@ -299,6 +313,8 @@ impl BatchVotesPublisher {
             .last_signed_batch_number
             .set(attestation.msg.number.0);
 
-        self.0.update(attesters, &[Arc::new(attestation)]).await
+        self.0
+            .update(attesters, genesis, &[Arc::new(attestation)])
+            .await
     }
 }
diff --git a/node/actors/network/src/gossip/mod.rs b/node/actors/network/src/gossip/mod.rs
index d3af5f4a..f5afd92b 100644
--- a/node/actors/network/src/gossip/mod.rs
+++ b/node/actors/network/src/gossip/mod.rs
@@ -154,6 +154,7 @@ impl Network {
         let Some(attesters) = self.genesis().attesters.as_ref() else {
             return Ok(());
         };
+        let genesis = self.genesis().hash();
         let mut sub = self.batch_votes.subscribe();
         loop {
             // In the future when we might be gossiping about multiple batches at the same time,
@@ -161,7 +162,7 @@ impl Network {
             // on L1 and we can finally increase the minimum as well.
             let quorums = {
                 let votes = sync::changed(ctx, &mut sub).await?;
-                votes.find_quorums(attesters, |_| false)
+                votes.find_quorums(attesters, &genesis, |_| false)
             };
 
             for qc in quorums {
diff --git a/node/actors/network/src/gossip/runner.rs b/node/actors/network/src/gossip/runner.rs
index ff36888c..2596ccd7 100644
--- a/node/actors/network/src/gossip/runner.rs
+++ b/node/actors/network/src/gossip/runner.rs
@@ -68,6 +68,7 @@ impl rpc::Handler<rpc::push_batch_votes::Rpc> for &PushServer<'_> {
             .batch_votes
             .update(
                 self.net.genesis().attesters.as_ref().context("attesters")?,
+                &self.net.genesis().hash(),
                 &req.0,
             )
             .await?;
diff --git a/node/actors/network/src/gossip/tests/mod.rs b/node/actors/network/src/gossip/tests/mod.rs
index 7a11f093..6811071f 100644
--- a/node/actors/network/src/gossip/tests/mod.rs
+++ b/node/actors/network/src/gossip/tests/mod.rs
@@ -116,10 +116,12 @@ fn mk_batch<R: Rng>(
     rng: &mut R,
     key: &attester::SecretKey,
     number: attester::BatchNumber,
+    genesis: attester::GenesisHash,
 ) -> attester::Signed<attester::Batch> {
     key.sign_msg(attester::Batch {
         number,
         hash: rng.gen(),
+        genesis,
     })
 }
 
@@ -138,10 +140,12 @@ fn random_netaddr<R: Rng>(
 fn random_batch_vote<R: Rng>(
     rng: &mut R,
     key: &attester::SecretKey,
+    genesis: attester::GenesisHash,
 ) -> Arc<attester::Signed<attester::Batch>> {
     let batch = attester::Batch {
         number: attester::BatchNumber(rng.gen_range(0..1000)),
         hash: rng.gen(),
+        genesis,
     };
     Arc::new(key.sign_msg(batch.to_owned()))
 }
@@ -170,6 +174,7 @@ fn update_signature<R: Rng>(
     let batch = attester::Batch {
         number: attester::BatchNumber((batch.number.0 as i64 + batch_number_diff) as u64),
         hash: rng.gen(),
+        genesis: batch.genesis,
     };
     Arc::new(key.sign_msg(batch.to_owned()))
 }
@@ -554,12 +559,17 @@ async fn test_batch_votes() {
     let votes = BatchVotesWatch::default();
     let mut sub = votes.subscribe();
 
+    let genesis = rng.gen::<attester::GenesisHash>();
+
     // Initial values.
     let mut want = Signatures::default();
     for k in &keys[0..6] {
-        want.insert(random_batch_vote(rng, k));
+        want.insert(random_batch_vote(rng, k, genesis));
     }
-    votes.update(&attesters, &want.as_vec()).await.unwrap();
+    votes
+        .update(&attesters, &genesis, &want.as_vec())
+        .await
+        .unwrap();
     assert_eq!(want.0, sub.borrow_and_update().votes);
 
     // newer batch number, should be updated
@@ -569,10 +579,10 @@ async fn test_batch_votes() {
     // older batch number, should be ignored
     let k4v2 = update_signature(rng, &want.get(&keys[4]).msg, &keys[4], -1);
     // first entry for a key in the config, should be inserted
-    let k6v1 = random_batch_vote(rng, &keys[6]);
+    let k6v1 = random_batch_vote(rng, &keys[6], genesis);
     // entry for a key outside of the config, should be ignored
     let k8 = rng.gen();
-    let k8v1 = random_batch_vote(rng, &k8);
+    let k8v1 = random_batch_vote(rng, &k8, genesis);
 
     // Update the ones we expect to succeed
     want.insert(k0v2.clone());
@@ -588,7 +598,7 @@ async fn test_batch_votes() {
         // no entry at all for keys[7]
         k8v1.clone(),
     ];
-    votes.update(&attesters, &update).await.unwrap();
+    votes.update(&attesters, &genesis, &update).await.unwrap();
     assert_eq!(want.0, sub.borrow_and_update().votes);
 
     // Invalid signature, should be rejected.
@@ -596,14 +606,32 @@ async fn test_batch_votes() {
         rng,
         &keys[1],
         attester::BatchNumber(want.get(&keys[0]).msg.number.0 + 1),
+        genesis,
     );
     k0v3.key = keys[0].public();
-    assert!(votes.update(&attesters, &[Arc::new(k0v3)]).await.is_err());
+    assert!(votes
+        .update(&attesters, &genesis, &[Arc::new(k0v3)])
+        .await
+        .is_err());
+
+    // Invalid genesis, should be rejected.
+    let other_genesis = rng.gen();
+    let k1v3 = mk_batch(
+        rng,
+        &keys[1],
+        attester::BatchNumber(want.get(&keys[1]).msg.number.0 + 1),
+        other_genesis,
+    );
+    assert!(votes
+        .update(&attesters, &genesis, &[Arc::new(k1v3)])
+        .await
+        .is_err());
+
     assert_eq!(want.0, sub.borrow_and_update().votes);
 
     // Duplicate entry in the update, should be rejected.
     assert!(votes
-        .update(&attesters, &[k8v1.clone(), k8v1])
+        .update(&attesters, &genesis, &[k8v1.clone(), k8v1])
         .await
         .is_err());
     assert_eq!(want.0, sub.borrow_and_update().votes);
@@ -627,7 +655,9 @@ fn test_batch_votes_quorum() {
         let batch1 = attester::Batch {
             number: batch0.number.next(),
             hash: rng.gen(),
+            genesis: batch0.genesis,
         };
+        let genesis = batch0.genesis;
         let mut batches = [(batch0, 0u64), (batch1, 0u64)];
 
         let mut votes = BatchVotes::default();
@@ -636,12 +666,14 @@ fn test_batch_votes_quorum() {
             let b = usize::from(rng.gen_range(0..100) < 80);
             let batch = &batches[b].0;
             let vote = sk.sign_msg(batch.clone());
-            votes.update(&attesters, &[Arc::new(vote)]).unwrap();
+            votes
+                .update(&attesters, &genesis, &[Arc::new(vote)])
+                .unwrap();
             batches[b].1 += attesters.weight(&sk.public()).unwrap();
 
             // Check that as soon as we have quorum it's found.
             if batches[b].1 >= attesters.threshold() {
-                let qs = votes.find_quorums(&attesters, |_| false);
+                let qs = votes.find_quorums(&attesters, &genesis, |_| false);
                 assert!(!qs.is_empty(), "should find quorum");
                 assert!(qs[0].message == *batch);
                 assert!(qs[0].signatures.keys().count() > 0);
@@ -655,11 +687,13 @@ fn test_batch_votes_quorum() {
         {
             // Check that a quorum can be skipped
             assert!(votes
-                .find_quorums(&attesters, |b| b == quorum.number)
+                .find_quorums(&attesters, &genesis, |b| b == quorum.number)
                 .is_empty());
         } else {
             // Check that if there was no quoroum then we don't find any.
-            assert!(votes.find_quorums(&attesters, |_| false).is_empty());
+            assert!(votes
+                .find_quorums(&attesters, &genesis, |_| false)
+                .is_empty());
         }
 
         // Check that the minimum batch number prunes data.
@@ -707,6 +741,7 @@ async fn test_batch_votes_propagation() {
         let batch = attester::Batch {
             number: batch.number,
             hash: rng.gen(),
+            genesis: setup.genesis.hash(),
         };
 
         // Start all nodes.
@@ -730,7 +765,7 @@ async fn test_batch_votes_propagation() {
         for (node, key) in nodes.iter().zip(setup.attester_keys.iter()) {
             node.net
                 .batch_vote_publisher()
-                .publish(attesters, key, batch.clone())
+                .publish(attesters, &setup.genesis.hash(), key, batch.clone())
                 .await
                 .unwrap();
         }
diff --git a/node/libs/roles/src/attester/conv.rs b/node/libs/roles/src/attester/conv.rs
index e3beec41..7eb3c065 100644
--- a/node/libs/roles/src/attester/conv.rs
+++ b/node/libs/roles/src/attester/conv.rs
@@ -27,14 +27,16 @@ impl ProtoFmt for Batch {
     type Proto = proto::Batch;
     fn read(r: &Self::Proto) -> anyhow::Result<Self> {
         Ok(Self {
-            hash: read_required(&r.hash).context("hash")?,
             number: BatchNumber(*required(&r.number).context("number")?),
+            hash: read_required(&r.hash).context("hash")?,
+            genesis: read_required(&r.genesis).context("genesis")?,
         })
     }
     fn build(&self) -> Self::Proto {
         Self::Proto {
             number: Some(self.number.0),
             hash: Some(self.hash.build()),
+            genesis: Some(self.genesis.build()),
         }
     }
 }
diff --git a/node/libs/roles/src/attester/messages/batch.rs b/node/libs/roles/src/attester/messages/batch.rs
index 0b88b709..e9554314 100644
--- a/node/libs/roles/src/attester/messages/batch.rs
+++ b/node/libs/roles/src/attester/messages/batch.rs
@@ -1,4 +1,4 @@
-use super::Signed;
+use super::{GenesisHash, Signed};
 use crate::{
     attester,
     validator::{Genesis, Payload},
@@ -92,6 +92,12 @@ pub struct Batch {
     pub number: BatchNumber,
     /// Hash of the batch.
     pub hash: BatchHash,
+    /// Hash of the genesis.
+    ///
+    /// This includes the chain ID and the current fork number, which prevents
+    /// replay attacks from other chains where the same attesters might operate,
+    /// or from earlier forks, which are created after a revert of L1 batches.
+    pub genesis: GenesisHash,
 }
 
 /// A certificate for a batch of L2 blocks to be sent to L1.
diff --git a/node/libs/roles/src/attester/messages/mod.rs b/node/libs/roles/src/attester/messages/mod.rs
index bd68233d..3c28e750 100644
--- a/node/libs/roles/src/attester/messages/mod.rs
+++ b/node/libs/roles/src/attester/messages/mod.rs
@@ -2,5 +2,6 @@
 mod batch;
 mod msg;
 
+pub use crate::validator::GenesisHash;
 pub use batch::*;
 pub use msg::*;
diff --git a/node/libs/roles/src/attester/testonly.rs b/node/libs/roles/src/attester/testonly.rs
index b4e53f79..ce56f3ad 100644
--- a/node/libs/roles/src/attester/testonly.rs
+++ b/node/libs/roles/src/attester/testonly.rs
@@ -52,6 +52,7 @@ impl Distribution<Batch> for Standard {
         Batch {
             number: rng.gen(),
             hash: rng.gen(),
+            genesis: rng.gen(),
         }
     }
 }
diff --git a/node/libs/roles/src/proto/attester/messages.proto b/node/libs/roles/src/proto/attester/messages.proto
index 1d117cdd..b6b40ec8 100644
--- a/node/libs/roles/src/proto/attester/messages.proto
+++ b/node/libs/roles/src/proto/attester/messages.proto
@@ -18,6 +18,7 @@ message BatchHash {
 message Batch {
   optional uint64 number = 1; // required
   optional BatchHash hash = 2; // required
+  optional validator.GenesisHash genesis = 3; // required
 }
 
 message BatchQC {
diff --git a/node/libs/storage/src/testonly/in_memory.rs b/node/libs/storage/src/testonly/in_memory.rs
index 9cb583a4..084da660 100644
--- a/node/libs/storage/src/testonly/in_memory.rs
+++ b/node/libs/storage/src/testonly/in_memory.rs
@@ -20,6 +20,7 @@ struct BlockStoreInner {
 
 #[derive(Debug)]
 struct BatchStoreInner {
+    genesis: validator::Genesis,
     persisted: sync::watch::Sender<BatchStoreState>,
     batches: Mutex<VecDeque<attester::SyncBatch>>,
     certs: Mutex<HashMap<attester::BatchNumber, attester::BatchQC>>,
@@ -69,8 +70,9 @@ impl BlockStore {
 
 impl BatchStore {
     /// New In-memory `BatchStore`.
-    pub fn new(first: attester::BatchNumber) -> Self {
+    pub fn new(genesis: validator::Genesis, first: attester::BatchNumber) -> Self {
         Self(Arc::new(BatchStoreInner {
+            genesis,
             persisted: sync::watch::channel(BatchStoreState { first, last: None }).0,
             batches: Mutex::default(),
             certs: Mutex::default(),
@@ -167,6 +169,7 @@ impl PersistentBatchStore for BatchStore {
         Ok(Some(attester::Batch {
             number,
             hash: attester::BatchHash(hash),
+            genesis: self.0.genesis.hash(),
         }))
     }
 
diff --git a/node/libs/storage/src/testonly/mod.rs b/node/libs/storage/src/testonly/mod.rs
index 38c4a4ba..a6329ba8 100644
--- a/node/libs/storage/src/testonly/mod.rs
+++ b/node/libs/storage/src/testonly/mod.rs
@@ -89,7 +89,7 @@ impl TestMemoryStorage {
         first: validator::BlockNumber,
     ) -> Self {
         let im_blocks = in_memory::BlockStore::new(genesis.clone(), first);
-        let im_batches = in_memory::BatchStore::new(attester::BatchNumber(0));
+        let im_batches = in_memory::BatchStore::new(genesis.clone(), attester::BatchNumber(0));
         Self::new_with_im(ctx, im_blocks, im_batches).await
     }
 
diff --git a/node/libs/storage/src/tests.rs b/node/libs/storage/src/tests.rs
index 36266bba..11fa5431 100644
--- a/node/libs/storage/src/tests.rs
+++ b/node/libs/storage/src/tests.rs
@@ -32,7 +32,7 @@ async fn test_inmemory_batch_store() {
     let mut setup = Setup::new(rng, 3);
     setup.push_batches(rng, 5);
 
-    let store = &testonly::in_memory::BatchStore::new(BatchNumber(0));
+    let store = &testonly::in_memory::BatchStore::new(setup.genesis.clone(), BatchNumber(0));
     let mut want = vec![];
     for batch in &setup.batches {
         store.queue_next_batch(ctx, batch.clone()).await.unwrap();