diff --git a/xfa/fwl/cfwl_widget.cpp b/xfa/fwl/cfwl_widget.cpp
index a252cd2..39b706b 100644
--- a/xfa/fwl/cfwl_widget.cpp
+++ b/xfa/fwl/cfwl_widget.cpp
@@ -45,6 +45,7 @@
 }
 
 CFWL_Widget::~CFWL_Widget() {
+  CHECK(!IsLocked());  // Prefer hard stop to UaF.
   NotifyDriver();
   m_pWidgetMgr->RemoveWidget(this);
 }