diff --git a/src/include/gpxe/settings_ui.h b/src/include/gpxe/settings_ui.h
index 01b8f172..70ee8cb3 100644
--- a/src/include/gpxe/settings_ui.h
+++ b/src/include/gpxe/settings_ui.h
@@ -9,6 +9,6 @@
 
 struct config_context;
 
-extern int settings_ui ( struct config_context *context );
+extern int settings_ui ( struct config_context *context ) __nonnull;
 
 #endif /* _GPXE_SETTINGS_UI_H */