diff --git a/gtk/css/gtkcssenums.h b/gtk/css/gtkcssenums.h
index 5470a61e51..8674696b3a 100644
--- a/gtk/css/gtkcssenums.h
+++ b/gtk/css/gtkcssenums.h
@@ -73,7 +73,8 @@ typedef enum
 typedef enum
 {
   GTK_CSS_PARSER_WARNING_DEPRECATED,
-  GTK_CSS_PARSER_WARNING_SYNTAX
+  GTK_CSS_PARSER_WARNING_SYNTAX,
+  GTK_CSS_PARSER_WARNING_UNIMPLEMENTED
 } GtkCssParserWarning;
 
 #endif /* __GTK_CSS_ENUMS_H__ */