diff --git a/lib/blockchain/chain.js b/lib/blockchain/chain.js
index e5e6ba75..24d550f3 100644
--- a/lib/blockchain/chain.js
+++ b/lib/blockchain/chain.js
@@ -1825,7 +1825,7 @@ Chain.prototype.getProgress = function getProgress() {
 /**
  * Calculate chain locator (an array of hashes).
  * @method
- * @param {Hash} start - Height or hash to treat as the tip.
+ * @param {Hash?} start - Height or hash to treat as the tip.
  * The current tip will be used if not present. Note that this can be a
  * non-existent hash, which is useful for headers-first locators.
  * @returns {Promise} - Returns {@link Hash}[].