diff --git a/src/matrix/e2ee/DecryptionResult.ts b/src/matrix/e2ee/DecryptionResult.ts
index 67c242bc..7735856a 100644
--- a/src/matrix/e2ee/DecryptionResult.ts
+++ b/src/matrix/e2ee/DecryptionResult.ts
@@ -43,7 +43,7 @@ export class DecryptionResult {
         public readonly claimedEd25519Key: string
     ) {}
 
-    setDevice(device: DeviceIdentity) {
+    setDevice(device: DeviceIdentity): void {
         this.device = device;
     }