diff --git a/packages/plugin-ext/src/common/proxy-handler.ts b/packages/plugin-ext/src/common/proxy-handler.ts
index dcfe7d4a2e722..5b2adb3d154ef 100644
--- a/packages/plugin-ext/src/common/proxy-handler.ts
+++ b/packages/plugin-ext/src/common/proxy-handler.ts
@@ -25,11 +25,19 @@ export interface RpcHandlerOptions {
 }
 export interface ProxyHandlerOptions extends RpcHandlerOptions {
     channelProvider: () => Promise<Channel>,
+    initCallback: InitializationCallback,
 }
 
 export interface InvocationHandlerOptions extends RpcHandlerOptions {
     target: any
 }
+
+export interface InitializationCallback {
+    reportInit(id: string): void
+    reportInitDone(id: string): void
+    checkInit(): Promise<void>
+}
+
 /**
  * A proxy handler that will send any method invocation on the proxied object
  * as a rcp protocol message over a channel.
@@ -40,6 +48,7 @@ export class ClientProxyHandler<T extends object> implements ProxyHandler<T> {
 
     readonly id: string;
     private readonly channelProvider: () => Promise<Channel>;
+    private readonly initCallback: InitializationCallback;
     private readonly encoder: RpcMessageEncoder;
     private readonly decoder: RpcMessageDecoder;
 
@@ -50,11 +59,13 @@ export class ClientProxyHandler<T extends object> implements ProxyHandler<T> {
     private initializeRpc(): void {
         // we need to set the flag to true before waiting for the channel provider. Otherwise `get` might
         // get called again and we'll try to open a channel more than once
+        this.initCallback.reportInit(this.id);
         this.isRpcInitialized = true;
         const clientOptions: RpcProtocolOptions = { encoder: this.encoder, decoder: this.decoder, mode: 'clientOnly' };
         this.channelProvider().then(channel => {
             const rpc = new RpcProtocol(channel, undefined, clientOptions);
             this.rpcDeferred.resolve(rpc);
+            this.initCallback.reportInitDone(this.id);
         });
     }
 
@@ -69,13 +80,13 @@ export class ClientProxyHandler<T extends object> implements ProxyHandler<T> {
         const isNotify = this.isNotification(name);
         return (...args: any[]) => {
             const method = name.toString();
-            return this.rpcDeferred.promise.then(async (connection: RpcProtocol) => {
+            return this.initCallback.checkInit().then(() => this.rpcDeferred.promise.then(async (connection: RpcProtocol) => {
                 if (isNotify) {
                     connection.sendNotification(method, args);
                 } else {
                     return await connection.sendRequest(method, args) as Promise<any>;
                 }
-            });
+            }));
         };
     }
 
diff --git a/packages/plugin-ext/src/common/rpc-protocol.ts b/packages/plugin-ext/src/common/rpc-protocol.ts
index 107c639ef2c60..fdb71bce887d1 100644
--- a/packages/plugin-ext/src/common/rpc-protocol.ts
+++ b/packages/plugin-ext/src/common/rpc-protocol.ts
@@ -27,11 +27,12 @@ import { Emitter, Event } from '@theia/core/lib/common/event';
 import { ChannelMultiplexer, MessageProvider } from '@theia/core/lib/common/message-rpc/channel';
 import { MsgPackMessageDecoder, MsgPackMessageEncoder } from '@theia/core/lib/common/message-rpc/rpc-message-encoder';
 import { Uint8ArrayReadBuffer, Uint8ArrayWriteBuffer } from '@theia/core/lib/common/message-rpc/uint8-array-message-buffer';
-import { ClientProxyHandler, RpcInvocationHandler } from './proxy-handler';
+import { ClientProxyHandler, InitializationCallback, RpcInvocationHandler } from './proxy-handler';
 import { MsgPackExtensionManager } from '@theia/core/lib/common/message-rpc/msg-pack-extension-manager';
 import { URI as VSCodeURI } from '@theia/core/shared/vscode-uri';
 import { BinaryBuffer } from '@theia/core/lib/common/buffer';
 import { Range, Position } from '../plugin/types-impl';
+import { Deferred } from '@theia/core/lib/common/promise-util';
 
 export interface MessageConnection {
     send(msg: string): void;
@@ -83,6 +84,7 @@ export class RPCProtocolImpl implements RPCProtocol {
     private readonly multiplexer: ChannelMultiplexer;
     private readonly encoder = new MsgPackMessageEncoder();
     private readonly decoder = new MsgPackMessageDecoder();
+    private readonly initCallback: InitializationCallback;
 
     private readonly toDispose = new DisposableCollection(
         Disposable.create(() => { /* mark as no disposed */ })
@@ -91,6 +93,7 @@ export class RPCProtocolImpl implements RPCProtocol {
     constructor(channel: Channel) {
         this.toDispose.push(this.multiplexer = new ChannelMultiplexer(new BatchingChannel(channel)));
         this.toDispose.push(Disposable.create(() => this.proxies.clear()));
+        this.initCallback = new InitializationCallbackImpl();
     }
 
     dispose(): void {
@@ -114,7 +117,9 @@ export class RPCProtocolImpl implements RPCProtocol {
     }
 
     protected createProxy<T>(proxyId: string): T {
-        const handler = new ClientProxyHandler({ id: proxyId, encoder: this.encoder, decoder: this.decoder, channelProvider: () => this.multiplexer.open(proxyId) });
+        const handler = new ClientProxyHandler({
+            id: proxyId, encoder: this.encoder, decoder: this.decoder, channelProvider: () => this.multiplexer.open(proxyId), initCallback: this.initCallback
+        });
         return new Proxy(Object.create(null), handler);
     }
 
@@ -149,6 +154,32 @@ export class RPCProtocolImpl implements RPCProtocol {
     }
 }
 
+export class InitializationCallbackImpl implements InitializationCallback {
+
+    private readonly runningInits = new Set<string>();
+
+    private checkInitDeferred: Deferred<void> = new Deferred();
+
+    reportInit(id: string): void {
+        if (this.runningInits.size === 0) {
+            this.checkInitDeferred = new Deferred();
+        }
+        this.runningInits.add(id);
+    }
+
+    reportInitDone(id: string): void {
+        this.runningInits.delete(id);
+        if (this.runningInits.size === 0) {
+            this.checkInitDeferred.resolve();
+        }
+    }
+
+    checkInit(): Promise<void> {
+        return this.checkInitDeferred.promise;
+    }
+
+}
+
 /**
  * Wraps and underlying channel to send/receive multiple messages in one go:
  *  - multiple messages to be sent from one stack get sent in bulk at `process.nextTick`.