diff --git a/src/mbyte.c b/src/mbyte.c
index ff165fa..a006312 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -701,6 +701,7 @@
 		     * where mblen() returns 0 for invalid character.
 		     * Therefore, following condition includes 0.
 		     */
+		    (void)mblen(NULL, 0);	/* First reset the state. */
 		    if (mblen(buf, (size_t)1) <= 0)
 			n = 2;
 		    else