diff --git a/server/src/rpc.ts b/server/src/rpc.ts
index ee5f600ec..473c526b1 100644
--- a/server/src/rpc.ts
+++ b/server/src/rpc.ts
@@ -109,8 +109,14 @@ class RpcProxy implements PrimitiveProxyHandler<any> {
     }
 
     set(target: any, p: string | symbol, value: any, receiver: any): boolean {
-        if (p === RpcPeer.finalizerIdSymbol)
+        if (p === RpcPeer.finalizerIdSymbol) {
             this.entry.finalizerId = value;
+        }
+        else {
+            this.proxyProps ||= {};
+            this.proxyProps[p] = value;
+        }
+        
         return true;
     }
 
diff --git a/server/test/rpc-proxy-set.ts b/server/test/rpc-proxy-set.ts
new file mode 100644
index 000000000..fb49d304f
--- /dev/null
+++ b/server/test/rpc-proxy-set.ts
@@ -0,0 +1,23 @@
+import { RpcPeer } from "../src/rpc";
+
+const p1 = new RpcPeer('p1', 'p2', message => {
+    p2.handleMessage(message);
+});
+
+const p2 = new RpcPeer('p2', 'p1', message => {
+    p1.handleMessage(message);
+});
+
+class Foo {
+}
+
+p1.params['thing'] = new Foo();
+
+async function test() {
+    const foo = await p2.getParam('thing');
+    foo.bar = 3;
+    if (foo.bar !== 3)
+        throw new Error('proxy custom property set failed');
+}
+
+test();