diff --git a/packages/playwright-core/src/server/injected/highlight.ts b/packages/playwright-core/src/server/injected/highlight.ts
index c06e58f529..5720ffc539 100644
--- a/packages/playwright-core/src/server/injected/highlight.ts
+++ b/packages/playwright-core/src/server/injected/highlight.ts
@@ -90,7 +90,8 @@ export class Highlight {
   }
 
   install() {
-    if (!this._injectedScript.document.documentElement.contains(this._glassPaneElement))
+    // NOTE: document.documentElement can be null: https://github.com/microsoft/TypeScript/issues/50078
+    if (this._injectedScript.document.documentElement && !this._injectedScript.document.documentElement.contains(this._glassPaneElement))
       this._injectedScript.document.documentElement.appendChild(this._glassPaneElement);
   }