diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md
index dde1610ba..86d0bd14c 100644
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@@ -309,7 +309,7 @@ Set `attestation.data = attestation_data` where `attestation_data` is the `Attes
 
 * Let `aggregation_bitfield` be a byte array filled with zeros of length `(len(committee) + 7) // 8`.
 * Let `index_into_committee` be the index into the validator's `committee` at which `validator_index` is located.
-* Set `participation_bitfield[index_into_committee // 8] |= 2 ** (index_into_committee % 8)`.
+* Set `aggregation_bitfield[index_into_committee // 8] |= 2 ** (index_into_committee % 8)`.
 * Set `attestation.participation_bitfield = participation_bitfield`.
 
 _Note_: Calling `get_attestation_participants(state, attestation.data, attestation.participation_bitfield)` should return `[validator_index]`.