diff --git a/include/stdlib.h b/include/stdlib.h
index 97ce5a7..d2c911f 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -76,7 +76,8 @@ size_t wcstombs (char *__restrict, const wchar_t *__restrict, size_t);
 #define EXIT_FAILURE 1
 #define EXIT_SUCCESS 0
 
-#define MB_CUR_MAX ((size_t)+4)
+size_t __ctype_get_mb_cur_max(void);
+#define MB_CUR_MAX (__ctype_get_mb_cur_max())
 
 #define RAND_MAX (0x7fffffff)
 
diff --git a/src/ctype/__ctype_get_mb_cur_max.c b/src/ctype/__ctype_get_mb_cur_max.c
index d235f4d..94b0bd4 100644
--- a/src/ctype/__ctype_get_mb_cur_max.c
+++ b/src/ctype/__ctype_get_mb_cur_max.c
@@ -1,6 +1,7 @@
 #include <stddef.h>
+#include "locale_impl.h"
 
 size_t __ctype_get_mb_cur_max()
 {
-	return 4;
+	return MB_CUR_MAX;
 }
diff --git a/src/internal/locale_impl.h b/src/internal/locale_impl.h
index f15e156..7577b51 100644
--- a/src/internal/locale_impl.h
+++ b/src/internal/locale_impl.h
@@ -33,3 +33,6 @@ const char *__lctrans_cur(const char *);
 
 #undef MB_CUR_MAX
 #define MB_CUR_MAX (CURRENT_UTF8 ? 4 : 1)
+
+#define CODEUNIT(c) (0xdfff & (signed char)(c))
+#define IS_CODEUNIT(c) ((unsigned)(c)-0xdf80 < 0x80)
\ No newline at end of file
diff --git a/src/internal/stdio_impl.h b/src/internal/stdio_impl.h
index e1325fe..72c5519 100644
--- a/src/internal/stdio_impl.h
+++ b/src/internal/stdio_impl.h
@@ -47,6 +47,7 @@ struct _IO_FILE {
 	unsigned char *shend;
 	off_t shlim, shcnt;
 	FILE *prev_locked, *next_locked;
+	struct __locale_struct *locale;
 };
 
 size_t __stdio_read(FILE *, unsigned char *, size_t);
diff --git a/src/locale/iconv.c b/src/locale/iconv.c
index e6121ae..1eeea94 100644
--- a/src/locale/iconv.c
+++ b/src/locale/iconv.c
@@ -5,6 +5,7 @@
 #include <stdlib.h>
 #include <limits.h>
 #include <stdint.h>
+#include "locale_impl.h"
 
 #define UTF_32BE    0300
 #define UTF_16LE    0301
@@ -165,9 +166,12 @@ size_t iconv(iconv_t cd0, char **restrict in, size_t *restrict inb, char **restr
 	int err;
 	unsigned char type = map[-1];
 	unsigned char totype = tomap[-1];
+	locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
 
 	if (!in || !*in || !*inb) return 0;
 
+	*ploc = UTF8_LOCALE;
+
 	for (; *inb; *in+=l, *inb-=l) {
 		c = *(unsigned char *)*in;
 		l = 1;
@@ -431,6 +435,7 @@ size_t iconv(iconv_t cd0, char **restrict in, size_t *restrict inb, char **restr
 			break;
 		}
 	}
+	*ploc = loc;
 	return x;
 ilseq:
 	err = EILSEQ;
@@ -445,5 +450,6 @@ starved:
 	x = -1;
 end:
 	errno = err;
+	*ploc = loc;
 	return x;
 }
diff --git a/src/locale/langinfo.c b/src/locale/langinfo.c
index a1ada24..776b447 100644
--- a/src/locale/langinfo.c
+++ b/src/locale/langinfo.c
@@ -33,7 +33,8 @@ char *__nl_langinfo_l(nl_item item, locale_t loc)
 	int idx = item & 65535;
 	const char *str;
 
-	if (item == CODESET) return "UTF-8";
+	if (item == CODESET)
+		return MB_CUR_MAX==1 ? "UTF-8-CODE-UNITS" : "UTF-8";
 	
 	switch (cat) {
 	case LC_NUMERIC:
diff --git a/src/multibyte/btowc.c b/src/multibyte/btowc.c
index 9d2c3b1..dc088a2 100644
--- a/src/multibyte/btowc.c
+++ b/src/multibyte/btowc.c
@@ -1,7 +1,10 @@
 #include <stdio.h>
 #include <wchar.h>
+#include "locale_impl.h"
 
 wint_t btowc(int c)
 {
-	return c<128U ? c : EOF;
+	if (c+1U <= 128) return c;
+	if (MB_CUR_MAX==1) return CODEUNIT(c);
+	return WEOF;
 }
diff --git a/src/multibyte/mbrtowc.c b/src/multibyte/mbrtowc.c
index e7b3654..40e2e1a 100644
--- a/src/multibyte/mbrtowc.c
+++ b/src/multibyte/mbrtowc.c
@@ -6,6 +6,7 @@
 
 #include <wchar.h>
 #include <errno.h>
+#include "locale_impl.h"
 #include "internal.h"
 
 size_t mbrtowc(wchar_t *restrict wc, const char *restrict src, size_t n, mbstate_t *restrict st)
@@ -27,6 +28,7 @@ size_t mbrtowc(wchar_t *restrict wc, const char *restrict src, size_t n, mbstate
 	if (!n) return -2;
 	if (!c) {
 		if (*s < 0x80) return !!(*wc = *s);
+		if (MB_CUR_MAX==1) return (*wc = CODEUNIT(*s)), 1;
 		if (*s-SA > SB-SA) goto ilseq;
 		c = bittab[*s++-SA]; n--;
 	}
diff --git a/src/multibyte/mbsrtowcs.c b/src/multibyte/mbsrtowcs.c
index 3c1343a..eb8f72a 100644
--- a/src/multibyte/mbsrtowcs.c
+++ b/src/multibyte/mbsrtowcs.c
@@ -7,6 +7,8 @@
 #include <stdint.h>
 #include <wchar.h>
 #include <errno.h>
+#include <string.h>
+#include "locale_impl.h"
 #include "internal.h"
 
 size_t mbsrtowcs(wchar_t *restrict ws, const char **restrict src, size_t wn, mbstate_t *restrict st)
@@ -24,6 +26,23 @@ size_t mbsrtowcs(wchar_t *restrict ws, const char **restrict src, size_t wn, mbs
 		}
 	}
 
+	if (MB_CUR_MAX==1) {
+		if (!ws) return strlen((const char *)s);
+		for (;;) {
+			if (!wn) {
+				*src = (const void *)s;
+				return wn0;
+			}
+			if (!*s) break;
+			c = *s++;
+			*ws++ = CODEUNIT(c);
+			wn--;
+		}
+		*ws = 0;
+		*src = 0;
+		return wn0-wn;
+	}
+
 	if (!ws) for (;;) {
 		if (*s-1u < 0x7f && (uintptr_t)s%4 == 0) {
 			while (!(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) {
diff --git a/src/multibyte/mbtowc.c b/src/multibyte/mbtowc.c
index 803d221..c147754 100644
--- a/src/multibyte/mbtowc.c
+++ b/src/multibyte/mbtowc.c
@@ -6,6 +6,7 @@
 
 #include <wchar.h>
 #include <errno.h>
+#include "locale_impl.h"
 #include "internal.h"
 
 int mbtowc(wchar_t *restrict wc, const char *restrict src, size_t n)
@@ -19,6 +20,7 @@ int mbtowc(wchar_t *restrict wc, const char *restrict src, size_t n)
 	if (!wc) wc = &dummy;
 
 	if (*s < 0x80) return !!(*wc = *s);
+	if (MB_CUR_MAX==1) return (*wc = CODEUNIT(*s)), 1;
 	if (*s-SA > SB-SA) goto ilseq;
 	c = bittab[*s++-SA];
 
diff --git a/src/multibyte/wcrtomb.c b/src/multibyte/wcrtomb.c
index 59f733d..75c972c 100644
--- a/src/multibyte/wcrtomb.c
+++ b/src/multibyte/wcrtomb.c
@@ -6,6 +6,7 @@
 
 #include <wchar.h>
 #include <errno.h>
+#include "locale_impl.h"
 
 size_t wcrtomb(char *restrict s, wchar_t wc, mbstate_t *restrict st)
 {
@@ -13,6 +14,13 @@ size_t wcrtomb(char *restrict s, wchar_t wc, mbstate_t *restrict st)
 	if ((unsigned)wc < 0x80) {
 		*s = wc;
 		return 1;
+	} else if (MB_CUR_MAX == 1) {
+		if (!IS_CODEUNIT(wc)) {
+			errno = EILSEQ;
+			return -1;
+		}
+		*s = wc;
+		return 1;
 	} else if ((unsigned)wc < 0x800) {
 		*s++ = 0xc0 | (wc>>6);
 		*s = 0x80 | (wc&0x3f);
diff --git a/src/multibyte/wctob.c b/src/multibyte/wctob.c
index d6353ee..412e3c8 100644
--- a/src/multibyte/wctob.c
+++ b/src/multibyte/wctob.c
@@ -1,8 +1,10 @@
 #include <stdio.h>
 #include <wchar.h>
+#include "locale_impl.h"
 
 int wctob(wint_t c)
 {
 	if (c < 128U) return c;
+	if (MB_CUR_MAX==1 && IS_CODEUNIT(c)) return (unsigned char)c;
 	return EOF;
 }
diff --git a/src/stdio/fgetwc.c b/src/stdio/fgetwc.c
index 8626d54..e455cfe 100644
--- a/src/stdio/fgetwc.c
+++ b/src/stdio/fgetwc.c
@@ -1,8 +1,9 @@
 #include "stdio_impl.h"
+#include "locale_impl.h"
 #include <wchar.h>
 #include <errno.h>
 
-wint_t __fgetwc_unlocked(FILE *f)
+static wint_t __fgetwc_unlocked_internal(FILE *f)
 {
 	mbstate_t st = { 0 };
 	wchar_t wc;
@@ -10,8 +11,6 @@ wint_t __fgetwc_unlocked(FILE *f)
 	unsigned char b;
 	size_t l;
 
-	f->mode |= f->mode+1;
-
 	/* Convert character from buffer if possible */
 	if (f->rpos < f->rend) {
 		l = mbrtowc(&wc, (void *)f->rpos, f->rend - f->rpos, &st);
@@ -39,6 +38,16 @@ wint_t __fgetwc_unlocked(FILE *f)
 	return wc;
 }
 
+wint_t __fgetwc_unlocked(FILE *f)
+{
+	locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
+	if (f->mode <= 0) fwide(f, 1);
+	*ploc = f->locale;
+	wchar_t wc = __fgetwc_unlocked_internal(f);
+	*ploc = loc;
+	return wc;
+}
+
 wint_t fgetwc(FILE *f)
 {
 	wint_t c;
diff --git a/src/stdio/fputwc.c b/src/stdio/fputwc.c
index 7b621dd..a1c8ac8 100644
--- a/src/stdio/fputwc.c
+++ b/src/stdio/fputwc.c
@@ -1,4 +1,5 @@
 #include "stdio_impl.h"
+#include "locale_impl.h"
 #include <wchar.h>
 #include <limits.h>
 #include <ctype.h>
@@ -7,8 +8,10 @@ wint_t __fputwc_unlocked(wchar_t c, FILE *f)
 {
 	char mbc[MB_LEN_MAX];
 	int l;
+	locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
 
-	f->mode |= f->mode+1;
+	if (f->mode <= 0) fwide(f, 1);
+	*ploc = f->locale;
 
 	if (isascii(c)) {
 		c = putc_unlocked(c, f);
@@ -20,6 +23,7 @@ wint_t __fputwc_unlocked(wchar_t c, FILE *f)
 		l = wctomb(mbc, c);
 		if (l < 0 || __fwritex((void *)mbc, l, f) < l) c = WEOF;
 	}
+	*ploc = loc;
 	return c;
 }
 
diff --git a/src/stdio/fputws.c b/src/stdio/fputws.c
index 5723cbc..0ed02f1 100644
--- a/src/stdio/fputws.c
+++ b/src/stdio/fputws.c
@@ -1,23 +1,28 @@
 #include "stdio_impl.h"
+#include "locale_impl.h"
 #include <wchar.h>
 
 int fputws(const wchar_t *restrict ws, FILE *restrict f)
 {
 	unsigned char buf[BUFSIZ];
 	size_t l=0;
+	locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
 
 	FLOCK(f);
 
-	f->mode |= f->mode+1;
+	fwide(f, 1);
+	*ploc = f->locale;
 
 	while (ws && (l = wcsrtombs((void *)buf, (void*)&ws, sizeof buf, 0))+1 > 1)
 		if (__fwritex(buf, l, f) < l) {
 			FUNLOCK(f);
+			*ploc = loc;
 			return -1;
 		}
 
 	FUNLOCK(f);
 
+	*ploc = loc;
 	return l; /* 0 or -1 */
 }
 
diff --git a/src/stdio/fwide.c b/src/stdio/fwide.c
index 8088e7a..8410b15 100644
--- a/src/stdio/fwide.c
+++ b/src/stdio/fwide.c
@@ -1,13 +1,14 @@
-#include <wchar.h>
 #include "stdio_impl.h"
-
-#define SH (8*sizeof(int)-1)
-#define NORMALIZE(x) ((x)>>SH | -((-(x))>>SH))
+#include "locale_impl.h"
 
 int fwide(FILE *f, int mode)
 {
 	FLOCK(f);
-	if (!f->mode) f->mode = NORMALIZE(mode);
+	if (mode) {
+		if (!f->locale) f->locale = MB_CUR_MAX==1
+			? C_LOCALE : UTF8_LOCALE;
+		if (!f->mode) f->mode = mode>0 ? 1 : -1;
+	}
 	mode = f->mode;
 	FUNLOCK(f);
 	return mode;
diff --git a/src/stdio/ungetwc.c b/src/stdio/ungetwc.c
index 394f92a..80d6e20 100644
--- a/src/stdio/ungetwc.c
+++ b/src/stdio/ungetwc.c
@@ -1,4 +1,5 @@
 #include "stdio_impl.h"
+#include "locale_impl.h"
 #include <wchar.h>
 #include <limits.h>
 #include <ctype.h>
@@ -8,15 +9,18 @@ wint_t ungetwc(wint_t c, FILE *f)
 {
 	unsigned char mbc[MB_LEN_MAX];
 	int l=1;
+	locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
 
 	FLOCK(f);
 
-	f->mode |= f->mode+1;
+	if (f->mode <= 0) fwide(f, 1);
+	*ploc = f->locale;
 
 	if (!f->rpos) __toread(f);
 	if (!f->rpos || f->rpos < f->buf - UNGET + l || c == WEOF ||
 	    (!isascii(c) && (l = wctomb((void *)mbc, c)) < 0)) {
 		FUNLOCK(f);
+		*ploc = loc;
 		return WEOF;
 	}
 
@@ -26,5 +30,6 @@ wint_t ungetwc(wint_t c, FILE *f)
 	f->flags &= ~F_EOF;
 
 	FUNLOCK(f);
+	*ploc = loc;
 	return c;
 }