diff --git a/packages/rate-limit/test/peer-ip.test.ts b/packages/rate-limit/test/peer-ip.test.ts
new file mode 100644
index 0000000..42c58da
--- /dev/null
+++ b/packages/rate-limit/test/peer-ip.test.ts
@@ -0,0 +1,123 @@
+// The default `keyOf` buckets callers by `ctx.ip`, so it is only as good as the address the serving
+// path hands it. Node's `listen()` has always filled `ctx.ip` from the socket. `serveDeno` and
+// `serveBun` left it as `''` until core #116 (merged in core #117), which put every caller in the
+// one `'unknown'` bucket: the first client to reach `max` locked out everybody else.
+//
+// So this runs over a real socket on each runtime, with the plugin's default `keyOf`, rather than
+// through `app.fetch` with a hand-written one — `app.fetch` has no peer, and a custom `keyOf` would
+// test the test. Two clients reach one dual-stack listener, one over IPv4 and one over IPv6, which is
+// the cheapest way to get two distinct peer addresses on one host.
+//
+// Against a core without #116 the Deno and Bun runs fail here, on purpose. Node is the control: its
+// path never had the bug and must stay green.
+import { strict as assert } from 'node:assert';
+import { createServer } from 'node:net';
+import type { AddressInfo } from 'node:net';
+import { test } from 'node:test';
+
+import { createApp, ctx, Get, Module, needs, Route } from '@green-tea/core';
+import type { App } from '@green-tea/core';
+
+import { rateLimit } from '../src/index.ts';
+import type { RateLimiter } from '../src/index.ts';
+
+@Route('/')
+class Probe {
+  @Get('/probe')
+  async probe(@needs('rateLimit') limit: RateLimiter, @ctx() context: { ip?: string }) {
+    await limit('signin');
+
+    return { ip: context.ip };
+  }
+}
+
+@Module({ mountpoint: '/', controllers: [Probe] })
+class ProbeModule {}
+
+/** A running server, whichever helper started it. */
+interface Served {
+  port: number;
+  close(): Promise<void>;
+}
+
+interface RuntimeGlobals {
+  Deno?: unknown;
+  Bun?: unknown;
+}
+
+/**
+ * Serves `app` on `hostname` through the helper this runtime actually uses in production.
+ *
+ * The adapters are imported lazily because each one only works on its own runtime. Node takes no
+ * hostname: `listen(port)` binds the unspecified address, which is dual-stack wherever IPv6 exists.
+ */
+async function serve(app: App, hostname: string): Promise<Served> {
+  const globals = globalThis as RuntimeGlobals;
+
+  if (globals.Deno) {
+    const { serveDeno } = await import('@green-tea/core/deno');
+    const server = await serveDeno(app, { hostname, port: 0, onListen: () => {} });
+    const { port } = (server as unknown as { addr: { port: number } }).addr;
+
+    return { port, close: () => server.close({ timeoutMs: 1_000 }) };
+  }
+
+  if (globals.Bun) {
+    const { serveBun } = await import('@green-tea/core/bun');
+    const server = await serveBun(app, { hostname, port: 0 });
+
+    return { port: server.port, close: () => server.close({ timeoutMs: 1_000 }) };
+  }
+
+  const server = await app.listen(0);
+
+  return { port: (server.address() as AddressInfo).port, close: () => app.close({ timeoutMs: 1_000 }) };
+}
+
+/** Whether this host can bind the IPv6 loopback at all; some CI containers cannot. */
+function ipv6Available(): Promise<boolean> {
+  return new Promise((resolve) => {
+    const probe = createServer();
+
+    probe.once('error', () => resolve(false));
+    probe.listen(0, '::1', () => probe.close(() => resolve(true)));
+  });
+}
+
+test('two peers on different addresses get separate budgets on the real serving path', async (t) => {
+  // Without IPv6, the fallback is two IPv4 loopback addresses. Every 127/8 address answers on Linux,
+  // which is what CI runs; macOS configures only 127.0.0.1, so there the fallback cannot connect.
+  const ipv6 = await ipv6Available();
+  const [hostname, a, b] = ipv6 ? ['::', '127.0.0.1', '[::1]'] : ['0.0.0.0', '127.0.0.1', '127.0.0.2'];
+
+  if (!ipv6) t.diagnostic('no IPv6 loopback: falling back to 127.0.0.1 and 127.0.0.2 (Linux only)');
+
+  const app = createApp({
+    modules: [ProbeModule],
+    plugins: [rateLimit({ rules: { signin: { windowMs: 60_000, max: 1, message: 'too many' } } })],
+  });
+  const server = await serve(app, hostname);
+  const hit = (host: string) => fetch(`http://${host}:${server.port}/probe`);
+
+  try {
+    const first = await hit(a);
+    assert.equal(first.status, 200);
+    const { ip: ipA } = (await first.json()) as { ip?: string };
+
+    assert.equal((await hit(a)).status, 429, 'client A was not limited at max: 1');
+
+    const other = await hit(b);
+    const body = (await other.text()) || '(empty body)';
+
+    // Checked before B's status so a regression names its cause: an empty `ctx.ip` is what folds both
+    // clients into one bucket, and the 429 that follows is only its symptom.
+    assert.ok(ipA, `ctx.ip was empty for client A on this serving path: ${JSON.stringify(ipA)}`);
+    assert.equal(other.status, 200, `client B shared client A's bucket (ctx.ip ${JSON.stringify(ipA)}): ${body}`);
+
+    const { ip: ipB } = JSON.parse(body) as { ip?: string };
+    assert.ok(ipB, 'ctx.ip was empty for client B');
+    assert.notEqual(ipA, ipB, 'both clients reported the same ctx.ip');
+  } finally {
+    await server.close();
+  }
+});