diff --git a/packages/ws-relay/src/index.ts b/packages/ws-relay/src/index.ts
index 53d02e2..1cc3915 100644
--- a/packages/ws-relay/src/index.ts
+++ b/packages/ws-relay/src/index.ts
@@ -33,7 +33,7 @@ type TransportState = {
     peer: Ref,
 };
 
-export function boot(ds: Ref, debug: boolean = false) {
+export function boot(ds: Ref, debug: boolean = false, WebSocketConstructor?: typeof WebSocket) {
     spawn named 'transportConnector' {
         at ds {
             during Observe({ "pattern": :pattern G.TransportConnection({
@@ -107,7 +107,7 @@ export function boot(ds: Ref, debug: boolean = false) {
             setTimeout(() => facet.turn(() => { stop {} }), 10000);
         }
         try {
-            const ws = new WebSocket(addr.url);
+            const ws = new (WebSocketConstructor ?? WebSocket)(addr.url);
             ws.binaryType = 'arraybuffer';
             ws.onopen = () => facet.turn(() => succeed(ws));
             ws.onclose = () => facet.turn(() => fail(Symbol.for('closed')));