diff --git a/crypto_kdf.js b/crypto_kdf.js
index d94d312..284c4bf 100644
--- a/crypto_kdf.js
+++ b/crypto_kdf.js
@@ -26,7 +26,7 @@ module.exports.crypto_kdf_derive_from_key = function crypto_kdf_derive_from_key
   var ctx_padded = new Uint8Array(blake2b.PERSONALBYTES)
   var salt = new Uint8Array(blake2b.SALTBYTES)
 
-  ctx_padded.set(ctx, 0, module.exports.crypto_kdf_CONTEXTBYTES)
+  ctx_padded.set(ctx, 0)
   STORE64_LE(salt, subkey_id)
 
   var outlen = Math.min(subkey.length, module.exports.crypto_kdf_BYTES_MAX)