diff --git a/src/platform/web/LegacyPlatform.js b/src/platform/web/LegacyPlatform.js
index e6bf7774..5cbfb52f 100644
--- a/src/platform/web/LegacyPlatform.js
+++ b/src/platform/web/LegacyPlatform.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import aesjs from "../../../lib/aes-js/index.js";
-import {hkdf} from "../../utils/crypto/hkdf.js";
+import {hkdf} from "../../utils/crypto/hkdf";
 import {Platform as ModernPlatform} from "./Platform.js";
 
 export function Platform(container, paths) {
diff --git a/src/utils/crypto/hkdf.js b/src/utils/crypto/hkdf.ts
similarity index 83%
rename from src/utils/crypto/hkdf.js
rename to src/utils/crypto/hkdf.ts
index d46dc496..25c1faf6 100644
--- a/src/utils/crypto/hkdf.js
+++ b/src/utils/crypto/hkdf.ts
@@ -6,8 +6,10 @@
  * Based on https://github.com/junkurihara/jscu/blob/develop/packages/js-crypto-hkdf/src/hkdf.ts
  */
 
+import type {Crypto} from "../../platform/web/dom/Crypto.js";
+
 // forked this code to make it use the cryptoDriver for HMAC that is more backwards-compatible
-export async function hkdf(cryptoDriver, key, salt, info, hash, length) {
+export async function hkdf(cryptoDriver: Crypto, key: Uint8Array, salt: Uint8Array, info: Uint8Array, hash: string, length: number): Promise<Uint8Array> {
     length = length / 8;
     const len = cryptoDriver.digestSize(hash);