diff --git a/crates/blockchain/src/lib.rs b/crates/blockchain/src/lib.rs
index ee6ccfdb..872e6aa6 100644
--- a/crates/blockchain/src/lib.rs
+++ b/crates/blockchain/src/lib.rs
@@ -279,7 +279,8 @@ impl BlockChainServer {
         &mut self,
         signed_block: SignedBlockWithAttestation,
     ) -> Result<(), StoreError> {
-        store::on_block(&mut self.store, signed_block)?;
+        let validator_ids = self.key_manager.validator_ids();
+        store::on_block(&mut self.store, signed_block, &validator_ids)?;
         metrics::update_head_slot(self.store.head_slot());
         metrics::update_latest_justified_slot(self.store.latest_justified().slot);
         metrics::update_latest_finalized_slot(self.store.latest_finalized().slot);
@@ -445,7 +446,8 @@ impl BlockChainServer {
             warn!("Received unaggregated attestation but node is not an aggregator");
             return;
         }
-        let _ = store::on_gossip_attestation(&mut self.store, attestation)
+        let validator_ids = self.key_manager.validator_ids();
+        let _ = store::on_gossip_attestation(&mut self.store, attestation, &validator_ids)
             .inspect_err(|err| warn!(%err, "Failed to process gossiped attestation"));
     }
 
diff --git a/crates/blockchain/src/store.rs b/crates/blockchain/src/store.rs
index 5a57c3df..03bd4f08 100644
--- a/crates/blockchain/src/store.rs
+++ b/crates/blockchain/src/store.rs
@@ -26,6 +26,16 @@ use crate::{INTERVALS_PER_SLOT, MILLISECONDS_PER_INTERVAL, MILLISECONDS_PER_SLOT
 
 const JUSTIFICATION_LOOKBACK_SLOTS: u64 = 3;
 
+/// Number of attestation committees per slot.
+/// With ATTESTATION_COMMITTEE_COUNT = 1, all validators are in subnet 0.
+const ATTESTATION_COMMITTEE_COUNT: u64 = 1;
+
+/// Compute the attestation subnet ID for a validator.
+#[allow(clippy::modulo_one)]
+fn compute_subnet_id(validator_id: u64) -> u64 {
+    validator_id % ATTESTATION_COMMITTEE_COUNT
+}
+
 /// Accept new aggregated payloads, promoting them to known for fork choice.
 fn accept_new_attestations(store: &mut Store, log_tree: bool) {
     store.promote_new_aggregated_payloads();
@@ -357,6 +367,7 @@ pub fn on_tick(
 pub fn on_gossip_attestation(
     store: &mut Store,
     signed_attestation: SignedAttestation,
+    local_validator_ids: &[u64],
 ) -> Result<(), StoreError> {
     let validator_id = signed_attestation.validator_id;
     let attestation = Attestation {
@@ -396,9 +407,16 @@ pub fn on_gossip_attestation(
     // Store attestation data by root (content-addressed, idempotent)
     store.insert_attestation_data_by_root(data_root, attestation.data.clone());
 
-    // Store gossip signature for later aggregation at interval 2.
-    store.insert_gossip_signature(data_root, attestation.data.slot, validator_id, signature);
-    metrics::update_gossip_signatures(store.gossip_signatures_count());
+    // Store gossip signature for later aggregation at interval 2,
+    // only if the attester is in the same subnet as one of our validators.
+    let attester_subnet = compute_subnet_id(validator_id);
+    let in_our_subnet = local_validator_ids
+        .iter()
+        .any(|&vid| compute_subnet_id(vid) == attester_subnet);
+    if in_our_subnet {
+        store.insert_gossip_signature(data_root, attestation.data.slot, validator_id, signature);
+        metrics::update_gossip_signatures(store.gossip_signatures_count());
+    }
 
     metrics::inc_attestations_valid();
 
@@ -506,8 +524,9 @@ pub fn on_gossip_aggregated_attestation(
 pub fn on_block(
     store: &mut Store,
     signed_block: SignedBlockWithAttestation,
+    local_validator_ids: &[u64],
 ) -> Result<(), StoreError> {
-    on_block_core(store, signed_block, true)
+    on_block_core(store, signed_block, true, local_validator_ids)
 }
 
 /// Process a new block without signature verification.
@@ -518,7 +537,7 @@ pub fn on_block_without_verification(
     store: &mut Store,
     signed_block: SignedBlockWithAttestation,
 ) -> Result<(), StoreError> {
-    on_block_core(store, signed_block, false)
+    on_block_core(store, signed_block, false, &[])
 }
 
 /// Core block processing logic.
@@ -529,6 +548,7 @@ fn on_block_core(
     store: &mut Store,
     signed_block: SignedBlockWithAttestation,
     verify: bool,
+    local_validator_ids: &[u64],
 ) -> Result<(), StoreError> {
     let _timing = metrics::time_fork_choice_block_processing();
 
@@ -633,16 +653,23 @@ fn on_block_core(
         };
         store.insert_new_aggregated_payload((proposer_vid, proposer_data_root), payload);
     } else {
-        // Store the proposer's signature for potential future block building
-        let proposer_sig =
-            ValidatorSignature::from_bytes(&signed_block.signature.proposer_signature)
-                .map_err(|_| StoreError::SignatureDecodingFailed)?;
-        store.insert_gossip_signature(
-            proposer_data_root,
-            proposer_attestation.data.slot,
-            proposer_vid,
-            proposer_sig,
-        );
+        // Store the proposer's signature for potential future block building,
+        // only if the proposer is in the same subnet as one of our validators.
+        let proposer_subnet = compute_subnet_id(proposer_vid);
+        let in_our_subnet = local_validator_ids
+            .iter()
+            .any(|&vid| compute_subnet_id(vid) == proposer_subnet);
+        if in_our_subnet {
+            let proposer_sig =
+                ValidatorSignature::from_bytes(&signed_block.signature.proposer_signature)
+                    .map_err(|_| StoreError::SignatureDecodingFailed)?;
+            store.insert_gossip_signature(
+                proposer_data_root,
+                proposer_attestation.data.slot,
+                proposer_vid,
+                proposer_sig,
+            );
+        }
     }
 
     info!(%slot, %block_root, %state_root, "Processed new block");
diff --git a/crates/blockchain/tests/signature_spectests.rs b/crates/blockchain/tests/signature_spectests.rs
index 5d617e33..c35c9ebe 100644
--- a/crates/blockchain/tests/signature_spectests.rs
+++ b/crates/blockchain/tests/signature_spectests.rs
@@ -55,7 +55,7 @@ fn run(path: &Path) -> datatest_stable::Result<()> {
         store::on_tick(&mut st, block_time_ms, true, false);
 
         // Process the block (this includes signature verification)
-        let result = store::on_block(&mut st, signed_block);
+        let result = store::on_block(&mut st, signed_block, &[]);
 
         // Step 3: Check that it succeeded or failed as expected
         match (result.is_ok(), test.expect_exception.as_ref()) {