--- ./src/multibyte/mbsnrtowcs.c	2017-08-08 16:19:29.311584832 +0300
+++ ./src/multibyte/mbsnrtowcs.c	2017-08-09 20:33:27.515980317 +0300
@@ -5,6 +5,7 @@
 	size_t l, cnt=0, n2;
 	wchar_t *ws, wbuf[256];
 	const char *s = *src;
+	const char *tmp_s;
 
 	if (!wcs) ws = wbuf, wn = sizeof wbuf / sizeof *wbuf;
 	else ws = wcs;
@@ -15,7 +16,7 @@
 
 	while ( s && wn && ( (n2=n/4)>=wn || n2>32 ) ) {
 		if (n2>=wn) n2=wn;
-		n -= n2;
+		tmp_s = s;
 		l = mbsrtowcs(ws, &s, n2, st);
 		if (!(l+1)) {
 			cnt = l;
@@ -26,6 +27,7 @@
 			ws += l;
 			wn -= l;
 		}
+		n = s ? n - (s - tmp_s) : 0;
 		cnt += l;
 	}
 	if (s) while (wn && n) {
--- ./src/multibyte/wcsnrtombs.c	2017-08-08 16:19:29.311584832 +0300
+++ ./src/multibyte/wcsnrtombs.c	2017-08-09 20:34:17.479978856 +0300
@@ -5,13 +5,14 @@
 	size_t l, cnt=0, n2;
 	char *s, buf[256];
 	const wchar_t *ws = *wcs;
+	const wchar_t *tmp_ws;
 
 	if (!dst) s = buf, n = sizeof buf;
 	else s = dst;
 
 	while ( ws && n && ( (n2=wn)>=n || n2>32 ) ) {
 		if (n2>=n) n2=n;
-		wn -= n2;
+		tmp_ws = ws;
 		l = wcsrtombs(s, &ws, n2, 0);
 		if (!(l+1)) {
 			cnt = l;
@@ -22,6 +23,7 @@
 			s += l;
 			n -= l;
 		}
+		wn = ws ? wn - (ws - tmp_ws) : 0;
 		cnt += l;
 	}
 	if (ws) while (n && wn) {