diff --git a/src/inspector/main_thread_interface.h b/src/inspector/main_thread_interface.h
index 3e8eb13645b009..a7d9f8a3c939d8 100644
--- a/src/inspector/main_thread_interface.h
+++ b/src/inspector/main_thread_interface.h
@@ -45,6 +45,7 @@ class MainThreadHandle : public std::enable_shared_from_this<MainThreadHandle> {
                             : main_thread_(main_thread) {
   }
   ~MainThreadHandle() {
+    Mutex::ScopedLock scoped_lock(block_lock_);
     CHECK_NULL(main_thread_);  // main_thread_ should have called Reset
   }
   std::unique_ptr<InspectorSession> Connect(