diff --git a/src/client.ts b/src/client.ts
index 5b87cbd75..6d270c149 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -8146,7 +8146,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return this.http.authedRequest(
             Method.Post, '/keys/signatures/upload', undefined,
             content, {
-                prefix: ClientPrefix.Unstable,
+                prefix: ClientPrefix.V3,
             },
         );
     }