diff --git a/CHANGES.md b/CHANGES.md
index a9216a3..145c3f8 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- `@openstatus/health`: `onReport` catches rejected promises from other JavaScript
+  realms without an unhandled rejection.
 - Health reports and responder fallbacks remain available when a rejected value
   cannot convert to a string. The error uses generic text without private fields.
 - Health responses ignore a top-level `toJSON` from `extend` so JSON
diff --git a/packages/health/src/check.test.ts b/packages/health/src/check.test.ts
index cba1530..5532b9f 100644
--- a/packages/health/src/check.test.ts
+++ b/packages/health/src/check.test.ts
@@ -1,6 +1,7 @@
 import assert from "node:assert/strict";
 import test from "node:test";
 import { setTimeout as delay } from "node:timers/promises";
+import { runInNewContext } from "node:vm";
 import { createHealthCheck } from "./check.ts";
 import { DuplicateProbeError } from "./errors.ts";
 import type { Probe } from "./types.ts";
@@ -150,6 +151,20 @@ test("createHealthCheck() swallows onReport errors", async () => {
   assert.equal((await rejecting.report()).status, "ok");
 });
 
+test("createHealthCheck() swallows onReport rejections from another realm", async () => {
+  const { probe } = counting("a");
+  const ForeignPromise: PromiseConstructor = runInNewContext("Promise");
+  assert.notEqual(ForeignPromise, Promise);
+  const check = createHealthCheck({
+    probes: [probe],
+    onReport: () => ForeignPromise.reject(new Error("logger down")),
+  });
+  const report = await check.report();
+  assert.equal(report.status, "ok");
+  await delay(0);
+  assert.equal(await check.report(), report);
+});
+
 test("createHealthCheck() accepts the formatError presets", async () => {
   const { probe } = counting("a", true);
   const generic = await createHealthCheck({ probes: [probe] }).report();
diff --git a/packages/health/src/check.ts b/packages/health/src/check.ts
index 8628c0f..57e02e6 100644
--- a/packages/health/src/check.ts
+++ b/packages/health/src/check.ts
@@ -59,8 +59,7 @@ export function createHealthCheck(options: HealthCheckOptions): HealthCheck {
 function notify(onReport: OnReport | undefined, report: HealthReport): void {
   if (onReport == null) return;
   try {
-    const result = onReport(report);
-    if (result instanceof Promise) result.catch(() => {});
+    Promise.resolve(onReport(report)).catch(() => {});
   } catch {
     return;
   }