diff --git a/include/stdlib.h b/include/stdlib.h
index f034c6e..fbe7a21 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/stdio_impl.h b/src/internal/stdio_impl.h
index 79be9fd..aafdc08 100644
--- a/src/internal/stdio_impl.h
+++ b/src/internal/stdio_impl.h
@@ -35,7 +35,8 @@ struct _IO_FILE {
 	int fd;
 	int pipe_pid;
 	long lockcount;
-	short dummy3;
+	unsigned char dummy3;
+	unsigned char utf8;
 	signed char mode;
 	signed char lbf;
 	int lock;
diff --git a/src/locale/iconv.c b/src/locale/iconv.c
index a0b0232..138d596 100644
--- a/src/locale/iconv.c
+++ b/src/locale/iconv.c
@@ -152,8 +152,10 @@ static void put_32(unsigned char *s, unsigned c, int e)
 }
 
 /* Adapt as needed */
-#define mbrtowc_utf8 mbrtowc
-#define wctomb_utf8 wctomb
+size_t __utf8rtowc(wchar_t *, const char *, size_t, mbstate_t *);
+size_t __wctoutf8(char *, wchar_t);
+#define mbrtowc_utf8 __utf8rtowc
+#define wctomb_utf8 __wctoutf8
 
 size_t iconv(iconv_t cd0, char **restrict in, size_t *restrict inb, char **restrict out, size_t *restrict outb)
 {
diff --git a/src/locale/langinfo.c b/src/locale/langinfo.c
index 13abf45..0b130e7 100644
--- a/src/locale/langinfo.c
+++ b/src/locale/langinfo.c
@@ -32,7 +32,7 @@ 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 loc->ctype_utf8 ? "UTF-8" : "ASCII+8BIT";
 	
 	switch (cat) {
 	case LC_NUMERIC:
diff --git a/src/multibyte/btowc.c b/src/multibyte/btowc.c
index 9d2c3b1..695964c 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 (unsigned char)c + 0x10f000;
+	return WEOF;
 }
diff --git a/src/multibyte/mbrtowc.c b/src/multibyte/mbrtowc.c
index e7b3654..c96d6e7 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 = *s + 0x10f000), 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..f4e46f3 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++ = c + (0x10f000 & -(c>>7));
+			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..6a2e3f9 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 = *s + 0x10f000), 1;
 	if (*s-SA > SB-SA) goto ilseq;
 	c = bittab[*s++-SA];
 
diff --git a/src/multibyte/utf8rtowc.c b/src/multibyte/utf8rtowc.c
new file mode 100644
index 0000000..6bb5220
--- /dev/null
+++ b/src/multibyte/utf8rtowc.c
@@ -0,0 +1,48 @@
+/* 
+ * This code was written by Rich Felker in 2010; no copyright is claimed.
+ * This code is in the public domain. Attribution is appreciated but
+ * unnecessary.
+ */
+
+#include <wchar.h>
+#include <errno.h>
+#include "internal.h"
+
+size_t __utf8rtowc(wchar_t *restrict wc, const char *restrict src, size_t n, mbstate_t *restrict st)
+{
+	unsigned c;
+	const unsigned char *s = (const void *)src;
+	const unsigned N = n;
+
+	c = *(unsigned *)st;
+	if (!wc) wc = (void *)&wc;
+
+	if (!n) return -2;
+	if (!c) {
+		if (*s < 0x80) return !!(*wc = *s);
+		if (*s-SA > SB-SA) goto ilseq;
+		c = bittab[*s++-SA]; n--;
+	}
+
+	if (n) {
+		if (OOB(c,*s)) goto ilseq;
+loop:
+		c = c<<6 | *s++-0x80; n--;
+		if (!(c&(1U<<31))) {
+			*(unsigned *)st = 0;
+			*wc = c;
+			return N-n;
+		}
+		if (n) {
+			if (*s-0x80u >= 0x40) goto ilseq;
+			goto loop;
+		}
+	}
+
+	*(unsigned *)st = c;
+	return -2;
+ilseq:
+	*(unsigned *)st = 0;
+	errno = EILSEQ;
+	return -1;
+}
diff --git a/src/multibyte/wcrtomb.c b/src/multibyte/wcrtomb.c
index 59f733d..0c7d0f0 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 ((unsigned)wc - 0x10f080 >= 0x80) {
+			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..c365016 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 && c-0x10f080U < 128) return (unsigned char)c;
 	return EOF;
 }
diff --git a/src/multibyte/wctoraw8.c b/src/multibyte/wctoraw8.c
new file mode 100644
index 0000000..24c4d8c
--- /dev/null
+++ b/src/multibyte/wctoraw8.c
@@ -0,0 +1,13 @@
+#include <wchar.h>
+#include <errno.h>
+
+int __wctoraw8(wchar_t wc)
+{
+	if ((unsigned)wc < 0x80) {
+		return wc;
+	} else if ((unsigned)wc - 0x10f080 < 0x80) {
+		return wc - 0x10f000;
+	}
+	errno = EILSEQ;
+	return -1;
+}
diff --git a/src/multibyte/wctoutf8.c b/src/multibyte/wctoutf8.c
new file mode 100644
index 0000000..bf05783
--- /dev/null
+++ b/src/multibyte/wctoutf8.c
@@ -0,0 +1,33 @@
+/* 
+ * This code was written by Rich Felker in 2010; no copyright is claimed.
+ * This code is in the public domain. Attribution is appreciated but
+ * unnecessary.
+ */
+
+#include <wchar.h>
+#include <errno.h>
+
+size_t __wctoutf8(char * s, wchar_t wc)
+{
+	if ((unsigned)wc < 0x80) {
+		*s = wc;
+		return 1;
+	} else if ((unsigned)wc < 0x800) {
+		*s++ = 0xc0 | (wc>>6);
+		*s = 0x80 | (wc&0x3f);
+		return 2;
+	} else if ((unsigned)wc < 0xd800 || (unsigned)wc-0xe000 < 0x2000) {
+		*s++ = 0xe0 | (wc>>12);
+		*s++ = 0x80 | ((wc>>6)&0x3f);
+		*s = 0x80 | (wc&0x3f);
+		return 3;
+	} else if ((unsigned)wc-0x10000 < 0x100000) {
+		*s++ = 0xf0 | (wc>>18);
+		*s++ = 0x80 | ((wc>>12)&0x3f);
+		*s++ = 0x80 | ((wc>>6)&0x3f);
+		*s = 0x80 | (wc&0x3f);
+		return 4;
+	}
+	errno = EILSEQ;
+	return -1;
+}
diff --git a/src/stdio/fgetwc.c b/src/stdio/fgetwc.c
index 8626d54..b3f10f9 100644
--- a/src/stdio/fgetwc.c
+++ b/src/stdio/fgetwc.c
@@ -2,6 +2,8 @@
 #include <wchar.h>
 #include <errno.h>
 
+size_t __utf8rtowc(wchar_t *, const char *, size_t, mbstate_t *);
+
 wint_t __fgetwc_unlocked(FILE *f)
 {
 	mbstate_t st = { 0 };
@@ -10,7 +12,14 @@ wint_t __fgetwc_unlocked(FILE *f)
 	unsigned char b;
 	size_t l;
 
-	f->mode |= f->mode+1;
+	if (!f->utf8) {
+		fwide(f, 1);
+		if (!f->utf8) {
+			c = getc_unlocked(f);
+			if (c >= 128) c += 0x10f000;
+			return c;
+		}
+	}
 
 	/* Convert character from buffer if possible */
 	if (f->rpos < f->rend) {
diff --git a/src/stdio/fputwc.c b/src/stdio/fputwc.c
index 7b621dd..dfb9b8d 100644
--- a/src/stdio/fputwc.c
+++ b/src/stdio/fputwc.c
@@ -3,14 +3,22 @@
 #include <limits.h>
 #include <ctype.h>
 
+int __wctoraw8(wchar_t);
+
 wint_t __fputwc_unlocked(wchar_t c, FILE *f)
 {
 	char mbc[MB_LEN_MAX];
 	int l;
 
-	f->mode |= f->mode+1;
+	if (!f->utf8) {
+		fwide(f, 1);
+		if (!f->utf8) {
+			c = __wctoraw8(c);
+			return c<0 ? WEOF : putc_unlocked(c, f);
+		}
+	}
 
-	if (isascii(c)) {
+	if (c < 128U) {
 		c = putc_unlocked(c, f);
 	} else if (f->wpos + MB_LEN_MAX < f->wend) {
 		l = wctomb((void *)f->wpos, c);
diff --git a/src/stdio/fwide.c b/src/stdio/fwide.c
index 8088e7a..0ebaff4 100644
--- a/src/stdio/fwide.c
+++ b/src/stdio/fwide.c
@@ -1,5 +1,6 @@
 #include <wchar.h>
 #include "stdio_impl.h"
+#include "locale_impl.h"
 
 #define SH (8*sizeof(int)-1)
 #define NORMALIZE(x) ((x)>>SH | -((-(x))>>SH))
@@ -7,7 +8,10 @@
 int fwide(FILE *f, int mode)
 {
 	FLOCK(f);
-	if (!f->mode) f->mode = NORMALIZE(mode);
+	if (!f->mode && mode) {
+		f->mode = NORMALIZE(mode);
+		f->utf8 = (MB_CUR_MAX > 1);
+	}
 	mode = f->mode;
 	FUNLOCK(f);
 	return mode;
diff --git a/src/stdio/ungetwc.c b/src/stdio/ungetwc.c
index 8cc85a6..2b6137e 100644
--- a/src/stdio/ungetwc.c
+++ b/src/stdio/ungetwc.c
@@ -4,6 +4,8 @@
 #include <ctype.h>
 #include <string.h>
 
+int __wctoraw8(wchar_t);
+
 wint_t ungetwc(wint_t c, FILE *f)
 {
 	unsigned char mbc[MB_LEN_MAX];
@@ -11,20 +13,25 @@ wint_t ungetwc(wint_t c, FILE *f)
 
 	if (c == WEOF) return c;
 
-	/* Try conversion early so we can fail without locking if invalid */
-	if (!isascii(c) && (l = wctomb((void *)mbc, c)) < 0)
-		return WEOF;
-
 	FLOCK(f);
 
-	f->mode |= f->mode+1;
+	if (!f->utf8) {
+		fwide(f, 1);
+		if (!f->utf8) {
+			c = __wctoraw8(c);
+			c = ungetc(c, f);
+			FUNLOCK(f);
+			return c;
+		}
+	}
 
-	if ((!f->rend && __toread(f)) || f->rpos < f->buf - UNGET + l) {
+	if ((c>=128U && (l = wctomb((void *)mbc, c)) < 0) ||
+	    (!f->rend && __toread(f)) || f->rpos < f->buf - UNGET + l) {
 		FUNLOCK(f);
 		return EOF;
 	}
 
-	if (isascii(c)) *--f->rpos = c;
+	if (c<128U) *--f->rpos = c;
 	else memcpy(f->rpos -= l, mbc, l);
 
 	f->flags &= ~F_EOF;
diff --git a/src/stdio/vfwprintf.c b/src/stdio/vfwprintf.c
index c640059..ec0565d 100644
--- a/src/stdio/vfwprintf.c
+++ b/src/stdio/vfwprintf.c
@@ -355,7 +355,7 @@ int vfwprintf(FILE *restrict f, const wchar_t *restrict fmt, va_list ap)
 	}
 
 	FLOCK(f);
-	f->mode |= f->mode+1;
+	fwide(f, 1);
 	ret = wprintf_core(f, fmt, &ap2, nl_arg, nl_type);
 	FUNLOCK(f);
 	va_end(ap2);
diff --git a/src/stdio/vfwscanf.c b/src/stdio/vfwscanf.c
index ac5c2c2..223aad4 100644
--- a/src/stdio/vfwscanf.c
+++ b/src/stdio/vfwscanf.c
@@ -104,7 +104,7 @@ int vfwscanf(FILE *restrict f, const wchar_t *restrict fmt, va_list ap)
 
 	FLOCK(f);
 
-	f->mode |= f->mode+1;
+	fwide(f, 1);
 
 	for (p=fmt; *p; p++) {