diff --git a/keyserver/src/socket/tunnelbroker-socket.js b/keyserver/src/socket/tunnelbroker-socket.js
index ac7b1d46b..e2ce21c04 100644
--- a/keyserver/src/socket/tunnelbroker-socket.js
+++ b/keyserver/src/socket/tunnelbroker-socket.js
@@ -1,192 +1,201 @@
 // @flow
 
 import uuid from 'uuid';
 import WebSocket from 'ws';
 
 import { tunnelbrokerHeartbeatTimeout } from 'lib/shared/timeouts.js';
 import type { ClientMessageToDevice } from 'lib/tunnelbroker/tunnelbroker-context.js';
 import type { MessageReceiveConfirmation } from 'lib/types/tunnelbroker/message-receive-confirmation-types.js';
 import type { MessageSentStatus } from 'lib/types/tunnelbroker/message-to-device-request-status-types.js';
 import type { MessageToDeviceRequest } from 'lib/types/tunnelbroker/message-to-device-request-types.js';
 import {
   type TunnelbrokerMessage,
   tunnelbrokerMessageTypes,
   tunnelbrokerMessageValidator,
 } from 'lib/types/tunnelbroker/messages.js';
 import {
   type RefreshKeyRequest,
   refreshKeysRequestValidator,
 } from 'lib/types/tunnelbroker/peer-to-peer-message-types.js';
 import type { ConnectionInitializationMessage } from 'lib/types/tunnelbroker/session-types.js';
 import type { Heartbeat } from 'lib/types/websocket/heartbeat-types.js';
 
 import { uploadNewOneTimeKeys } from '../utils/olm-utils.js';
 
 type PromiseCallbacks = {
   +resolve: () => void,
   +reject: (error: string) => void,
 };
 type Promises = { [clientMessageID: string]: PromiseCallbacks };
 
 class TunnelbrokerSocket {
   ws: WebSocket;
   connected: boolean;
   promises: Promises;
   heartbeatTimeoutID: ?TimeoutID;
+  oneTimeKeysPromise: ?Promise<void>;
 
   constructor(socketURL: string, initMessage: ConnectionInitializationMessage) {
     this.connected = false;
     this.promises = {};
 
     const socket = new WebSocket(socketURL);
 
     socket.on('open', () => {
       socket.send(JSON.stringify(initMessage));
     });
 
     socket.on('close', async () => {
       this.stopHeartbeatTimeout();
       this.connected = false;
       console.error('Connection to Tunnelbroker closed');
     });
 
     socket.on('error', (error: Error) => {
       console.error('Tunnelbroker socket error:', error.message);
     });
 
     socket.on('message', this.onMessage);
 
     this.ws = socket;
   }
 
   onMessage: (event: ArrayBuffer) => Promise<void> = async (
     event: ArrayBuffer,
   ) => {
     let rawMessage;
     try {
       rawMessage = JSON.parse(event.toString());
     } catch (e) {
       console.error('error while parsing Tunnelbroker message:', e.message);
       return;
     }
 
     if (!tunnelbrokerMessageValidator.is(rawMessage)) {
       console.error('invalid TunnelbrokerMessage: ', rawMessage.toString());
       return;
     }
     const message: TunnelbrokerMessage = rawMessage;
 
     this.resetHeartbeatTimeout();
 
     if (
       message.type ===
       tunnelbrokerMessageTypes.CONNECTION_INITIALIZATION_RESPONSE
     ) {
       if (message.status.type === 'Success' && !this.connected) {
         this.connected = true;
         console.info('session with Tunnelbroker created');
       } else if (message.status.type === 'Success' && this.connected) {
         console.info(
           'received ConnectionInitializationResponse with status: Success for already connected socket',
         );
       } else {
         this.connected = false;
         console.error(
           'creating session with Tunnelbroker error:',
           message.status.data,
         );
       }
     } else if (message.type === tunnelbrokerMessageTypes.MESSAGE_TO_DEVICE) {
       const confirmation: MessageReceiveConfirmation = {
         type: tunnelbrokerMessageTypes.MESSAGE_RECEIVE_CONFIRMATION,
         messageIDs: [message.messageID],
       };
       this.ws.send(JSON.stringify(confirmation));
 
       const { payload } = message;
       try {
         const messageToKeyserver = JSON.parse(payload);
         if (refreshKeysRequestValidator.is(messageToKeyserver)) {
           const request: RefreshKeyRequest = messageToKeyserver;
-          await uploadNewOneTimeKeys(request.numberOfKeys);
+          this.refreshOneTimeKeys(request.numberOfKeys);
         }
       } catch (e) {
         console.error(
           'error while processing message to keyserver:',
           e.message,
         );
       }
     } else if (
       message.type === tunnelbrokerMessageTypes.MESSAGE_TO_DEVICE_REQUEST_STATUS
     ) {
       for (const status: MessageSentStatus of message.clientMessageIDs) {
         if (status.type === 'Success') {
           if (this.promises[status.data]) {
             this.promises[status.data].resolve();
             delete this.promises[status.data];
           } else {
             console.log(
               'received successful response for a non-existent request',
             );
           }
         } else if (status.type === 'Error') {
           if (this.promises[status.data.id]) {
             this.promises[status.data.id].reject(status.data.error);
             delete this.promises[status.data.id];
           } else {
             console.log('received error response for a non-existent request');
           }
         } else if (status.type === 'SerializationError') {
           console.error('SerializationError for message: ', status.data);
         } else if (status.type === 'InvalidRequest') {
           console.log('Tunnelbroker recorded InvalidRequest');
         }
       }
     } else if (message.type === tunnelbrokerMessageTypes.HEARTBEAT) {
       const heartbeat: Heartbeat = {
         type: tunnelbrokerMessageTypes.HEARTBEAT,
       };
       this.ws.send(JSON.stringify(heartbeat));
     }
   };
 
+  refreshOneTimeKeys: (numberOfKeys: number) => void = numberOfKeys => {
+    const oldOneTimeKeysPromise = this.oneTimeKeysPromise;
+    this.oneTimeKeysPromise = (async () => {
+      await oldOneTimeKeysPromise;
+      await uploadNewOneTimeKeys(numberOfKeys);
+    })();
+  };
+
   sendMessage: (message: ClientMessageToDevice) => Promise<void> = (
     message: ClientMessageToDevice,
   ) => {
     if (!this.connected) {
       throw new Error('Tunnelbroker not connected');
     }
     const clientMessageID = uuid.v4();
     const messageToDevice: MessageToDeviceRequest = {
       type: tunnelbrokerMessageTypes.MESSAGE_TO_DEVICE_REQUEST,
       clientMessageID,
       deviceID: message.deviceID,
       payload: message.payload,
     };
 
     return new Promise((resolve, reject) => {
       this.promises[clientMessageID] = {
         resolve,
         reject,
       };
       this.ws.send(JSON.stringify(messageToDevice));
     });
   };
 
   stopHeartbeatTimeout() {
     if (this.heartbeatTimeoutID) {
       clearTimeout(this.heartbeatTimeoutID);
       this.heartbeatTimeoutID = null;
     }
   }
 
   resetHeartbeatTimeout() {
     this.stopHeartbeatTimeout();
     this.heartbeatTimeoutID = setTimeout(() => {
       this.ws.close();
       this.connected = false;
     }, tunnelbrokerHeartbeatTimeout);
   }
 }
 
 export default TunnelbrokerSocket;