diff --git a/fpdfsdk/cpdfsdk_widget.h b/fpdfsdk/cpdfsdk_widget.h
index f3bdc54..a1ff923 100644
--- a/fpdfsdk/cpdfsdk_widget.h
+++ b/fpdfsdk/cpdfsdk_widget.h
@@ -35,7 +35,7 @@
 class CXFA_FFWidgetHandler;
 #endif  // PDF_ENABLE_XFA
 
-class CPDFSDK_Widget : public CPDFSDK_BAAnnot {
+class CPDFSDK_Widget final : public CPDFSDK_BAAnnot {
  public:
 #ifdef PDF_ENABLE_XFA
   CXFA_FFWidget* GetMixXFAWidget() const;