diff --git a/src/encoding.ts b/src/encoding.ts
index cbf763b3..4cfeb3d5 100644
--- a/src/encoding.ts
+++ b/src/encoding.ts
@@ -6,7 +6,7 @@ export type TEncodingExtended = TEncoding | 'buffer';
 
 export const ENCODING_UTF8: TEncoding = 'utf8';
 
-export function assertEncoding(encoding: string) {
+export function assertEncoding(encoding: string | undefined) {
   if (encoding && !Buffer.isEncoding(encoding)) throw new errors.TypeError('ERR_INVALID_OPT_VALUE_ENCODING', encoding);
 }