diff --git a/src/errors.h b/src/errors.h
index 6d3d06d..da45df2 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -2944,7 +2944,7 @@
 EXTERN char e_missing_return_type[]
 	INIT(= N_("E1157: Missing return type"));
 EXTERN char e_cannot_use_flatten_in_vim9_script[]
-	INIT(= N_("E1158: Cannot use flatten() in Vim9 script"));
+	INIT(= N_("E1158: Cannot use flatten() in Vim9 script, use flattennew()"));
 #endif
 EXTERN char e_cannot_split_window_when_closing_buffer[]
 	INIT(= N_("E1159: Cannot split a window when closing the buffer"));