diff --git a/docs/api/js-utils.encode.md b/docs/api/js-utils.encode.md
index 665416e..129790c 100644
--- a/docs/api/js-utils.encode.md
+++ b/docs/api/js-utils.encode.md
@@ -9,7 +9,7 @@ Concatenate then encode a list of buffers.
 <b>Signature:</b>
 
 ```typescript
-export declare function encode(chunks: Array<Buffer>, encoding: string): string;
+export declare function encode(chunks: Array<Buffer>, encoding: AllowedBufferEncoding): string;
 ```
 
 ## Parameters
@@ -17,7 +17,7 @@ export declare function encode(chunks: Array<Buffer>, encoding: string): string;
 |  Parameter | Type | Description |
 |  --- | --- | --- |
 |  chunks | Array&lt;Buffer&gt; |  |
-|  encoding | string |  |
+|  encoding | AllowedBufferEncoding |  |
 
 <b>Returns:</b>
 
diff --git a/src/Buffer.ts b/src/Buffer.ts
index f336504..8bc0f8c 100644
--- a/src/Buffer.ts
+++ b/src/Buffer.ts
@@ -1,3 +1,5 @@
+export type AllowedBufferEncoding = 'ascii' | 'utf-8';
+
 /**
  * Concatenate a list of buffers.
  *
@@ -13,7 +15,7 @@ export function concat(chunks: Array<Buffer>): Buffer {
  *
  * @public
  */
-export function encode(chunks: Array<Buffer>, encoding: string): string {
+export function encode(chunks: Array<Buffer>, encoding: AllowedBufferEncoding): string {
   if (chunks.length === 0) {
     return '';
   }