diff --git a/CHANGELOG.md b/CHANGELOG.md
index becf83bc681..0c3d6bfe7ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ For experimental package changes, see the [experimental CHANGELOG](experimental/
 ### :bug: (Bug Fix)
 
 * fix(sdk-trace-web): fix invalid timings in span events [#4486](https://github.com/open-telemetry/opentelemetry-js/pull/4486) @Abinet18
+* fix(resources): ensure BrowserDetector does not think Node.js v21 is a browser [#4561](https://github.com/open-telemetry/opentelemetry-js/issues/4561) @trentm
 
 ### :books: (Refine Doc)
 
diff --git a/packages/opentelemetry-resources/src/detectors/BrowserDetectorSync.ts b/packages/opentelemetry-resources/src/detectors/BrowserDetectorSync.ts
index b58fea94c8e..66a48010671 100644
--- a/packages/opentelemetry-resources/src/detectors/BrowserDetectorSync.ts
+++ b/packages/opentelemetry-resources/src/detectors/BrowserDetectorSync.ts
@@ -24,7 +24,12 @@ import { diag } from '@opentelemetry/api';
  */
 class BrowserDetectorSync implements DetectorSync {
   detect(config?: ResourceDetectionConfig): IResource {
-    const isBrowser = typeof navigator !== 'undefined';
+    const isBrowser =
+      typeof navigator !== 'undefined' &&
+      global.process?.versions?.node === undefined && // Node.js v21 adds `navigator`
+      // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+      // @ts-ignore don't have Bun types
+      global.Bun?.version === undefined; // Bun (bun.sh) defines `navigator`
     if (!isBrowser) {
       return Resource.empty();
     }