diff --git a/packages/docusaurus/src/client/exports/__tests__/isInternalUrl.ts b/packages/docusaurus/src/client/exports/__tests__/isInternalUrl.ts
new file mode 100644
index 0000000000..bc0833dd89
--- /dev/null
+++ b/packages/docusaurus/src/client/exports/__tests__/isInternalUrl.ts
@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import isInternalUrl from '../isInternalUrl';
+
+describe('isInternalUrl', () => {
+  test('should be true for root relative links', () => {
+    expect(isInternalUrl('/foo/bar')).toBeTruthy();
+  });
+
+  test('should be true for relative links', () => {
+    expect(isInternalUrl('foo/bar')).toBeTruthy();
+  });
+
+  test('should be false for HTTP links', () => {
+    expect(isInternalUrl('http://foo.com')).toBeFalsy();
+  });
+
+  test('should be false for HTTPS links', () => {
+    expect(isInternalUrl('https://foo.com')).toBeFalsy();
+  });
+
+  test('should be false for whatever protocol links', () => {
+    expect(isInternalUrl('//foo.com')).toBeFalsy();
+  });
+});
diff --git a/packages/docusaurus/src/client/exports/isInternalUrl.js b/packages/docusaurus/src/client/exports/isInternalUrl.js
index ee15f12a60..182de277fe 100644
--- a/packages/docusaurus/src/client/exports/isInternalUrl.js
+++ b/packages/docusaurus/src/client/exports/isInternalUrl.js
@@ -6,5 +6,5 @@
  */
 
 export default function isInternalUrl(url) {
-  return /^\/(?!\/)/.test(url);
+  return /^(https?:|\/\/)/.test(url) === false;
 }