diff --git a/src/json.c b/src/json.c
index d6507c3..7256a8c 100644
--- a/src/json.c
+++ b/src/json.c
@@ -68,7 +68,12 @@
 		default:
 		    if (c >= 0x20)
 		    {
+#ifdef FEAT_MBYTE
 			numbuf[mb_char2bytes(c, numbuf)] = NUL;
+#else
+			numbuf[0] = c;
+			numbuf[1] = NUL;
+#endif
 			ga_concat(gap, numbuf);
 		    }
 		    else