diff --git a/index.d.ts b/index.d.ts
index f603626..73ac8f4 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -26,9 +26,10 @@ export function to_utf8(str: string, encoding: string): string;
  * encode a number to hex
  *
  * @param {number} n number to encode
+ * @param {number} padding minumum length of output
  * @returns {string} hex
  */
-export function num_to_hex(n: number): string;
+export function num_to_hex(n: number, padding?: number): string;
 /**
  * decode a number from hex
  *