diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 73789749b..3001f44bd 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1595,7 +1595,7 @@ All [validators](#dfn-validator):
 
 **Note**: `previous_epoch_boundary_attesting_balance` balance might be marginally different than `current_epoch_boundary_attesting_balance` during the previous epoch transition. Due to the tight bound on validator churn each epoch and small per-epoch rewards/penalties, the potential balance difference is very low and only marginally affects consensus safety.
 
-For every `shard_committee` in `state.shard_committees_at_slots`:
+For every `shard_committee_at_slot` in `state.shard_committees_at_slots` and for every `shard_committee` in `shard_committee_at_slot`:
 
 * Let `shard_block_root` be `state.latest_crosslinks[shard_committee.shard].shard_block_root`
 * Let `attesting_validator_indices(shard_committee, shard_block_root)` be the union of the [validator](#dfn-validator) index sets given by `[get_attestation_participants(state, a.data, a.participation_bitfield) for a in current_epoch_attestations + previous_epoch_attestations if a.shard == shard_committee.shard and a.shard_block_root == shard_block_root]`.