diff --git a/include/_ctype.h b/include/_ctype.h
--- a/include/_ctype.h
+++ b/include/_ctype.h
@@ -100,14 +100,14 @@
 __maskrune(__ct_rune_t _c, unsigned long _f)
 {
 	return ((_c < 0 || _c >= _CACHED_RUNES) ? ___runetype(_c) :
-		_CurrentRuneLocale->__runetype[_c]) & _f;
+		_CurrentRuneLocale->__runetype[_c & 0xff]) & _f;
 }
 
 static __inline int
 __sbmaskrune(__ct_rune_t _c, unsigned long _f)
 {
 	return (_c < 0 || _c >= __mb_sb_limit) ? 0 :
-	       _CurrentRuneLocale->__runetype[_c] & _f;
+	       _CurrentRuneLocale->__runetype[_c & 0xff] & _f;
 }
 
 static __inline int
@@ -126,35 +126,35 @@
 __isctype(__ct_rune_t _c, unsigned long _f)
 {
 	return (_c < 0 || _c >= 128) ? 0 :
-	       !!(_DefaultRuneLocale.__runetype[_c] & _f);
+	       !!(_DefaultRuneLocale.__runetype[_c & 0xff] & _f);
 }
 
 static __inline __ct_rune_t
 __toupper(__ct_rune_t _c)
 {
 	return (_c < 0 || _c >= _CACHED_RUNES) ? ___toupper(_c) :
-	       _CurrentRuneLocale->__mapupper[_c];
+	       _CurrentRuneLocale->__mapupper[_c & 0xff];
 }
 
 static __inline __ct_rune_t
 __sbtoupper(__ct_rune_t _c)
 {
 	return (_c < 0 || _c >= __mb_sb_limit) ? _c :
-	       _CurrentRuneLocale->__mapupper[_c];
+	       _CurrentRuneLocale->__mapupper[_c & 0xff];
 }
 
 static __inline __ct_rune_t
 __tolower(__ct_rune_t _c)
 {
 	return (_c < 0 || _c >= _CACHED_RUNES) ? ___tolower(_c) :
-	       _CurrentRuneLocale->__maplower[_c];
+	       _CurrentRuneLocale->__maplower[_c & 0xff];
 }
 
 static __inline __ct_rune_t
 __sbtolower(__ct_rune_t _c)
 {
 	return (_c < 0 || _c >= __mb_sb_limit) ? _c :
-	       _CurrentRuneLocale->__maplower[_c];
+	       _CurrentRuneLocale->__maplower[_c & 0xff];
 }
 
 static __inline int
diff --git a/include/xlocale/_ctype.h b/include/xlocale/_ctype.h
--- a/include/xlocale/_ctype.h
+++ b/include/xlocale/_ctype.h
@@ -80,7 +80,7 @@
 	int __limit;
 	_RuneLocale *runes = __runes_for_locale(__loc, &__limit);
 	return ((__c < 0 || __c >= _CACHED_RUNES) ? ___runetype_l(__c, __loc) :
-	        runes->__runetype[__c]) & __f;
+	        runes->__runetype[__c & 0xff]) & __f;
 }
 
 _XLOCALE_INLINE int
@@ -105,7 +105,7 @@
 	int __limit;
 	_RuneLocale *runes = __runes_for_locale(__loc, &__limit);
 	return (__c < 0 || __c >= __limit) ? 0 :
-	       runes->__runetype[__c] & __f;
+	       runes->__runetype[__c &0xff] & __f;
 }
 
 _XLOCALE_INLINE int
@@ -150,14 +150,14 @@
 	int __limit;
 	_RuneLocale *__runes = __runes_for_locale(__l, &__limit);
 	return (__c < 0 || __c >= _CACHED_RUNES) ? ___tolower_l(__c, __l) :
-	       __runes->__maplower[__c];
+	       __runes->__maplower[__c & 0xff];
 }
 _XLOCALE_INLINE int towupper_l(int __c, locale_t __l)
 {
 	int __limit;
 	_RuneLocale *__runes = __runes_for_locale(__l, &__limit);
 	return (__c < 0 || __c >= _CACHED_RUNES) ? ___toupper_l(__c, __l) :
-	       __runes->__mapupper[__c];
+	       __runes->__mapupper[__c & 0xff];
 }
 _XLOCALE_INLINE int
 __wcwidth_l(__ct_rune_t _c, locale_t __l)
@@ -190,14 +190,14 @@
 	int __limit;
 	_RuneLocale *__runes = __runes_for_locale(__l, &__limit);
 	return (__c < 0 || __c >= __limit) ? __c :
-	       __runes->__maplower[__c];
+	       __runes->__maplower[__c & 0xff];
 }
 _XLOCALE_INLINE int toupper_l(int __c, locale_t __l)
 {
 	int __limit;
 	_RuneLocale *__runes = __runes_for_locale(__l, &__limit);
 	return (__c < 0 || __c >= __limit) ? __c :
-	       __runes->__mapupper[__c];
+	       __runes->__mapupper[__c & 0xff];
 }
 #endif
 #endif /* (defined(_XLOCALE_WCTYPES) && !defined(_XLOCALE_WCTYPE_H)) || \