diff --git a/ui.h b/ui.h
index a0580b7..3b21774 100644
--- a/ui.h
+++ b/ui.h
@@ -31,10 +31,10 @@
     // Initialize the object; called before anything else.
     virtual void Init();
     // Show a stage indicator.  Call immediately after Init().
-    virtual void SetStage(int current, int max) { }
+    virtual void SetStage(int current, int max) = 0;
 
     // After calling Init(), you can tell the UI what locale it is operating in.
-    virtual void SetLocale(const char* locale) { }
+    virtual void SetLocale(const char* locale) = 0;
 
     // Set the overall recovery state ("background image").
     enum Icon { NONE, INSTALLING_UPDATE, ERASING, NO_COMMAND, ERROR };
@@ -65,6 +65,8 @@
     // toggled on the text display).
     virtual void Print(const char* fmt, ...) __printflike(2, 3) = 0;
 
+    virtual void ShowFile(const char* filename) = 0;
+
     // --- key handling ---
 
     // Wait for keypress and return it.  May return -1 after timeout.