diff --git a/specs/phase0/beacon-chain.md b/specs/phase0/beacon-chain.md
index 34ce3c9c5..b47558484 100644
--- a/specs/phase0/beacon-chain.md
+++ b/specs/phase0/beacon-chain.md
@@ -604,7 +604,7 @@ def bytes_to_uint64(data: bytes) -> uint64:
 
 The [IETF BLS signature draft standard v4](https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-04) with ciphersuite `BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_POP_` defines the following functions:
 
-- `def Sign(secret_key: int, message: Bytes) -> BLSSignature`
+- `def Sign(privkey: int, message: Bytes) -> BLSSignature`
 - `def Verify(pubkey: BLSPubkey, message: Bytes, signature: BLSSignature) -> bool`
 - `def Aggregate(signatures: Sequence[BLSSignature]) -> BLSSignature`
 - `def FastAggregateVerify(pubkeys: Sequence[BLSPubkey], message: Bytes, signature: BLSSignature) -> bool`