diff --git a/lib/toc_parse.y b/lib/toc_parse.y
index d62413d..9bd5fc4 100644
--- a/lib/toc_parse.y
+++ b/lib/toc_parse.y
@@ -264,7 +264,7 @@ languages
 	;
 
 language
-	: NUMBER ':' NUMBER opt_nl
+	: NUMBER ':' NUMBER opt_nl { /* not implemented */ }
 	;
 
 cdtext_langs