diff --git a/packages/plugin-ext/src/common/proxy-handler.ts b/packages/plugin-ext/src/common/proxy-handler.ts
index 5b2adb3d154ef..632a220fed9b3 100644
--- a/packages/plugin-ext/src/common/proxy-handler.ts
+++ b/packages/plugin-ext/src/common/proxy-handler.ts
@@ -25,17 +25,16 @@ export interface RpcHandlerOptions {
 }
 export interface ProxyHandlerOptions extends RpcHandlerOptions {
     channelProvider: () => Promise<Channel>,
-    initCallback: InitializationCallback,
+    proxySynchronizer: ProxySynchronizer,
 }
 
 export interface InvocationHandlerOptions extends RpcHandlerOptions {
     target: any
 }
 
-export interface InitializationCallback {
-    reportInit(id: string): void
-    reportInitDone(id: string): void
-    checkInit(): Promise<void>
+export interface ProxySynchronizer {
+    startProxyInitialization(id: string, init: Promise<void>): void
+    pendingProxyInitializations(): Promise<void>
 }
 
 /**
@@ -48,7 +47,7 @@ export class ClientProxyHandler<T extends object> implements ProxyHandler<T> {
 
     readonly id: string;
     private readonly channelProvider: () => Promise<Channel>;
-    private readonly initCallback: InitializationCallback;
+    private readonly proxySynchronizer: ProxySynchronizer;
     private readonly encoder: RpcMessageEncoder;
     private readonly decoder: RpcMessageDecoder;
 
@@ -59,13 +58,12 @@ 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.proxySynchronizer.startProxyInitialization(this.id, this.rpcDeferred.promise.then(() => { }));
         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);
         });
     }
 
@@ -80,7 +78,7 @@ export class ClientProxyHandler<T extends object> implements ProxyHandler<T> {
         const isNotify = this.isNotification(name);
         return (...args: any[]) => {
             const method = name.toString();
-            return this.initCallback.checkInit().then(() => this.rpcDeferred.promise.then(async (connection: RpcProtocol) => {
+            return this.proxySynchronizer.pendingProxyInitializations().then(() => this.rpcDeferred.promise.then(async (connection: RpcProtocol) => {
                 if (isNotify) {
                     connection.sendNotification(method, args);
                 } else {
diff --git a/packages/plugin-ext/src/common/rpc-protocol.ts b/packages/plugin-ext/src/common/rpc-protocol.ts
index 1a2aaa470a8ab..d58b4173c59e8 100644
--- a/packages/plugin-ext/src/common/rpc-protocol.ts
+++ b/packages/plugin-ext/src/common/rpc-protocol.ts
@@ -27,7 +27,7 @@ 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, InitializationCallback, RpcInvocationHandler } from './proxy-handler';
+import { ClientProxyHandler, ProxySynchronizer, 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';
@@ -84,7 +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 initCallback: ProxySynchronizer;
 
     private readonly toDispose = new DisposableCollection(
         Disposable.create(() => { /* mark as no disposed */ })
@@ -118,7 +118,7 @@ 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), initCallback: this.initCallback
+            id: proxyId, encoder: this.encoder, decoder: this.decoder, channelProvider: () => this.multiplexer.open(proxyId), proxySynchronizer: this.initCallback
         });
         return new Proxy(Object.create(null), handler);
     }
@@ -154,7 +154,7 @@ export class RPCProtocolImpl implements RPCProtocol {
     }
 }
 
-export class InitializationCallbackImpl implements InitializationCallback {
+export class InitializationCallbackImpl implements ProxySynchronizer {
 
     private readonly runningInits = new Set<string>();
 
@@ -166,21 +166,22 @@ export class InitializationCallbackImpl implements InitializationCallback {
         this.checkInitDeferred.resolve();
     }
 
-    reportInit(id: string): void {
+    startProxyInitialization(id: string, init: Promise<void>): void {
         if (this.runningInits.size === 0) {
             this.checkInitDeferred = new Deferred();
         }
+        init.then(() => this.finishProxyInitialization(id));
         this.runningInits.add(id);
     }
 
-    reportInitDone(id: string): void {
+    protected finishProxyInitialization(id: string): void {
         this.runningInits.delete(id);
         if (this.runningInits.size === 0) {
             this.checkInitDeferred.resolve();
         }
     }
 
-    checkInit(): Promise<void> {
+    pendingProxyInitializations(): Promise<void> {
         return this.checkInitDeferred.promise;
     }