diff --git a/packages/playwright-core/src/client/selectors.ts b/packages/playwright-core/src/client/selectors.ts
index 9720b838e61fd..3a34cef5a96ff 100644
--- a/packages/playwright-core/src/client/selectors.ts
+++ b/packages/playwright-core/src/client/selectors.ts
@@ -34,6 +34,9 @@ export class Selectors implements api.Selectors {
   }
 
   async register(name: string, script: string | (() => SelectorEngine) | { path?: string, content?: string }, options: { contentScript?: boolean } = {}): Promise<void> {
+    if (this._selectorEngines.some(engine => engine.name === name))
+      throw new Error(`selectors.register: "${name}" selector engine has been already registered`);
+
     const source = await evaluationScript(this._platform, script, undefined, false);
     const selectorEngine: channels.SelectorEngine = { ...options, name, source };
     for (const context of this._contextsForSelectors)
diff --git a/tests/library/selectors-register.spec.ts b/tests/library/selectors-register.spec.ts
index 4bc0305749c2f..83fb73971eedf 100644
--- a/tests/library/selectors-register.spec.ts
+++ b/tests/library/selectors-register.spec.ts
@@ -145,6 +145,11 @@ it('should handle errors', async ({ playwright, browser }) => {
   await page.close();
 });
 
+it('should throw "already registered" error when registering', { annotation: { type: 'issue', description: 'https://github.com/microsoft/playwright/issues/36467' } }, async ({ playwright }) => {
+  await playwright.selectors.register('alreadyRegistered', createTagSelector);
+  await expect(playwright.selectors.register('alreadyRegistered', createTagSelector)).rejects.toThrowError('selectors.register: "alreadyRegistered" selector engine has been already registered');
+});
+
 it('should not rely on engines working from the root', async ({ playwright, browser }) => {
   const page = await browser.newPage();
   const createValueEngine = () => ({