diff --git a/src/matrix/ssss/index.ts b/src/matrix/ssss/index.ts
index 15e95200..fa09228d 100644
--- a/src/matrix/ssss/index.ts
+++ b/src/matrix/ssss/index.ts
@@ -16,17 +16,13 @@ limitations under the License.
 
 import {KeyDescription, Key} from "./common";
 import {keyFromPassphrase} from "./passphrase";
-import {keyFromRecoveryKey} from "./recoveryKey.js";
+import {keyFromRecoveryKey} from "./recoveryKey";
 import {SESSION_E2EE_KEY_PREFIX} from "../e2ee/common.js";
 import type {Storage} from "../storage/idb/Storage";
 import type {Transaction} from "../storage/idb/Transaction";
 import type {IKeyDescription} from "./common";
 import type {Platform} from "../../platform/web/Platform.js";
-
-type Olm = {
-    PRIVATE_KEY_LENGTH: number;
-    [key: string]: any
-};
+import type { Olm } from "./recoveryKey";
 
 const SSSS_KEY = `${SESSION_E2EE_KEY_PREFIX}ssssKey`;
 
diff --git a/src/matrix/ssss/recoveryKey.js b/src/matrix/ssss/recoveryKey.ts
similarity index 80%
rename from src/matrix/ssss/recoveryKey.js
rename to src/matrix/ssss/recoveryKey.ts
index b1a746bc..1271a814 100644
--- a/src/matrix/ssss/recoveryKey.js
+++ b/src/matrix/ssss/recoveryKey.ts
@@ -14,8 +14,15 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 import {Key} from "./common";
+import {KeyDescription} from "./common";
+import type {Platform} from "../../platform/web/Platform.js";
 
-const OLM_RECOVERY_KEY_PREFIX = [0x8B, 0x01];
+export type Olm = {
+    PRIVATE_KEY_LENGTH: number;
+    [key: string]: any;
+};
+
+const OLM_RECOVERY_KEY_PREFIX = [0x8B, 0x01] as const;
 
 /**
  * @param  {Olm} olm
@@ -23,7 +30,7 @@ const OLM_RECOVERY_KEY_PREFIX = [0x8B, 0x01];
  * @param  {string} recoveryKey
  * @return {Key}
  */
-export function keyFromRecoveryKey(keyDescription, recoveryKey, olm, platform) {
+export function keyFromRecoveryKey(keyDescription: KeyDescription, recoveryKey: string, olm: Olm, platform: Platform): Key {
     const result = platform.encoding.base58.decode(recoveryKey.replace(/ /g, ''));
 
     let parity = 0;