diff --git a/ts_src/index.ts b/ts_src/index.ts
index d51b7d4..849d1b0 100644
--- a/ts_src/index.ts
+++ b/ts_src/index.ts
@@ -39,7 +39,10 @@ function salt(password?: string): string {
   return 'mnemonic' + (password || '');
 }
 
-export function mnemonicToSeedSync(mnemonic: string, password: string): Buffer {
+export function mnemonicToSeedSync(
+  mnemonic: string,
+  password?: string,
+): Buffer {
   const mnemonicBuffer = Buffer.from(
     (mnemonic || '').normalize('NFKD'),
     'utf8',
@@ -54,7 +57,7 @@ export function mnemonicToSeedSync(mnemonic: string, password: string): Buffer {
 
 export function mnemonicToSeed(
   mnemonic: string,
-  password: string,
+  password?: string,
 ): Promise<Buffer> {
   return new Promise(
     (resolve, reject): void => {
diff --git a/types/index.d.ts b/types/index.d.ts
index 69e0381..5c34d76 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,6 +1,6 @@
 /// <reference types="node" />
-export declare function mnemonicToSeedSync(mnemonic: string, password: string): Buffer;
-export declare function mnemonicToSeed(mnemonic: string, password: string): Promise<Buffer>;
+export declare function mnemonicToSeedSync(mnemonic: string, password?: string): Buffer;
+export declare function mnemonicToSeed(mnemonic: string, password?: string): Promise<Buffer>;
 export declare function mnemonicToEntropy(mnemonic: string, wordlist?: string[]): string;
 export declare function entropyToMnemonic(entropy: Buffer | string, wordlist?: string[]): string;
 export declare function generateMnemonic(strength?: number, rng?: (size: number) => Buffer, wordlist?: string[]): string;