diff --git a/xfa/fxfa/cxfa_ffapp.h b/xfa/fxfa/cxfa_ffapp.h
index f3a5c75..d26b90c 100644
--- a/xfa/fxfa/cxfa_ffapp.h
+++ b/xfa/fxfa/cxfa_ffapp.h
@@ -21,8 +21,8 @@
 class CXFA_FontMgr;
 class IFX_SeekableReadStream;
 
-class CXFA_FFApp : public cppgc::GarbageCollected<CXFA_FFApp>,
-                   public CFWL_App::AdapterIface {
+class CXFA_FFApp final : public cppgc::GarbageCollected<CXFA_FFApp>,
+                         public CFWL_App::AdapterIface {
  public:
   class CallbackIface {
    public: