diff --git a/substrate/primitives/io/src/lib.rs b/substrate/primitives/io/src/lib.rs
index 5d29fe5c94..4b520a240a 100644
--- a/substrate/primitives/io/src/lib.rs
+++ b/substrate/primitives/io/src/lib.rs
@@ -474,7 +474,10 @@ pub trait Crypto {
 	}
 
 	/// Verify and recover a SECP256k1 ECDSA signature.
-	/// - `sig` is passed in RSV format. V should be either 0/1 or 27/28.
+	///
+	/// - `sig` is passed in RSV format. V should be either `0/1` or `27/28`.
+	/// - `msg` is the blake2-256 hash of the message.
+	///
 	/// Returns `Err` if the signature is bad, otherwise the 64-byte pubkey
 	/// (doesn't include the 0x04 prefix).
 	fn secp256k1_ecdsa_recover(
@@ -493,8 +496,11 @@ pub trait Crypto {
 	}
 
 	/// Verify and recover a SECP256k1 ECDSA signature.
-	/// - `sig` is passed in RSV format. V should be either 0/1 or 27/28.
-	/// - returns `Err` if the signature is bad, otherwise the 33-byte compressed pubkey.
+	///
+	/// - `sig` is passed in RSV format. V should be either `0/1` or `27/28`.
+	/// - `msg` is the blake2-256 hash of the message.
+	///
+	/// Returns `Err` if the signature is bad, otherwise the 33-byte compressed pubkey.
 	fn secp256k1_ecdsa_recover_compressed(
 		sig: &[u8; 65],
 		msg: &[u8; 32],