diff --git a/beacon_node/beacon_chain/src/attestation_verification.rs b/beacon_node/beacon_chain/src/attestation_verification.rs
index 62e65d5f87a..3d722a534be 100644
--- a/beacon_node/beacon_chain/src/attestation_verification.rs
+++ b/beacon_node/beacon_chain/src/attestation_verification.rs
@@ -1309,10 +1309,11 @@ pub fn obtain_indexed_attestation_and_committees_per_slot<T: BeaconChainTypes>(
                 attesting_indices_electra::get_indexed_attestation(&committees, att)
                     .map(|attestation| (attestation, committees_per_slot))
                     .map_err(|e| {
-                        if e == BlockOperationError::BeaconStateError(NoCommitteeFound) {
+                        let index = att.committee_index();
+                        if e == BlockOperationError::BeaconStateError(NoCommitteeFound(index)) {
                             Error::NoCommitteeForSlotAndIndex {
                                 slot: att.data.slot,
-                                index: att.committee_index(),
+                                index,
                             }
                         } else {
                             Error::Invalid(e)
diff --git a/consensus/state_processing/src/common/get_attesting_indices.rs b/consensus/state_processing/src/common/get_attesting_indices.rs
index 595cc69f87c..9848840e96d 100644
--- a/consensus/state_processing/src/common/get_attesting_indices.rs
+++ b/consensus/state_processing/src/common/get_attesting_indices.rs
@@ -113,11 +113,15 @@ pub mod attesting_indices_electra {
             .map(|committee| (committee.index, committee))
             .collect();
 
+        let committee_count_per_slot = committees.len() as u64;
+        let mut participant_count = 0;
         for index in committee_indices {
             if let Some(&beacon_committee) = committees_map.get(&index) {
-                if aggregation_bits.len() != beacon_committee.committee.len() {
-                    return Err(BeaconStateError::InvalidBitfield);
+                // This check is new to the spec's `process_attestation` in Electra.
+                if index >= committee_count_per_slot {
+                    return Err(BeaconStateError::InvalidCommitteeIndex(index));
                 }
+                participant_count.safe_add_assign(beacon_committee.committee.len() as u64)?;
                 let committee_attesters = beacon_committee
                     .committee
                     .iter()
@@ -136,10 +140,13 @@ pub mod attesting_indices_electra {
 
                 committee_offset.safe_add(beacon_committee.committee.len())?;
             } else {
-                return Err(Error::NoCommitteeFound);
+                return Err(Error::NoCommitteeFound(index));
             }
+        }
 
-            // TODO(electra) what should we do when theres no committee found for a given index?
+        // This check is new to the spec's `process_attestation` in Electra.
+        if participant_count as usize != aggregation_bits.len() {
+            return Err(BeaconStateError::InvalidBitfield);
         }
 
         let mut indices = output.into_iter().collect_vec();
diff --git a/consensus/types/src/beacon_state.rs b/consensus/types/src/beacon_state.rs
index 599c0bfc39c..d9c7a78537a 100644
--- a/consensus/types/src/beacon_state.rs
+++ b/consensus/types/src/beacon_state.rs
@@ -159,7 +159,8 @@ pub enum Error {
     IndexNotSupported(usize),
     InvalidFlagIndex(usize),
     MerkleTreeError(merkle_proof::MerkleTreeError),
-    NoCommitteeFound,
+    NoCommitteeFound(CommitteeIndex),
+    InvalidCommitteeIndex(CommitteeIndex),
 }
 
 /// Control whether an epoch-indexed field can be indexed at the next epoch or not.