diff --git a/src/eval.c b/src/eval.c
index 9f6db31..b2f4462 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -12786,7 +12786,7 @@
 	    dict_add_nr_str(dict, "group", 0L, syn_id2name(cur->hlg_id));
 	    dict_add_nr_str(dict, "priority", (long)cur->priority, NULL);
 	    dict_add_nr_str(dict, "id", (long)cur->id, NULL);
-# ifdef FEAT_CONCEAL
+# if defined(FEAT_CONCEAL) && defined(FEAT_MBYTE)
 	    if (cur->conceal_char)
 	    {
 		char_u buf[MB_MAXBYTES + 1];