diff --git a/test/js/bun/http/proxy-stress-helpers.ts b/test/js/bun/http/proxy-stress-helpers.ts
index 24dd0e044378..9303240e6700 100644
--- a/test/js/bun/http/proxy-stress-helpers.ts
+++ b/test/js/bun/http/proxy-stress-helpers.ts
@@ -365,6 +365,11 @@ export async function createAdversarialProxy(opts: AdversarialProxyOptions = {})
       // and getaddrinfo want the bare literal.
       if (host.startsWith("[") && host.endsWith("]")) host = host.slice(1, -1);
 
+      // Origins bind 127.0.0.1 but advertise `localhost`; on darwin that
+      // resolves `::1` first, and v4/v6 ephemeral-port spaces are independent,
+      // so dial the bound address. IPv6-literal tests pass `[::1]` explicitly.
+      if (host === "localhost") host = "127.0.0.1";
+
       upstream = net.connect(port, host);
       let clientEnded = false;
       const endClient = () => {