diff --git a/include/_ctype.h b/include/_ctype.h
--- a/include/_ctype.h
+++ b/include/_ctype.h
@@ -92,8 +92,6 @@
 #define	__inline
 #endif
 
-extern int __mb_sb_limit;
-
 /*
  * Use inline functions if we are allowed to and the compiler supports them.
  */
@@ -102,6 +100,15 @@
 
 #include <runetype.h>
 
+#ifndef _LOCALE_T_DEFINED
+#define _LOCALE_T_DEFINED
+typedef struct  _xlocale *locale_t;
+#endif
+
+__BEGIN_DECLS
+_RuneLocale *__runes_for_locale(locale_t, int *);
+__END_DECLS
+
 static __inline int
 __maskrune(__ct_rune_t _c, unsigned long _f)
 {
@@ -112,7 +119,10 @@
 static __inline int
 __sbmaskrune(__ct_rune_t _c, unsigned long _f)
 {
-	return (_c < 0 || _c >= __mb_sb_limit) ? 0 :
+	int __limit;
+
+	(void) __runes_for_locale((locale_t)-2, &__limit);
+	return (_c < 0 || _c >= __limit) ? 0 :
 	       _CurrentRuneLocale->__runetype[_c] & _f;
 }
 
@@ -145,7 +155,10 @@
 static __inline __ct_rune_t
 __sbtoupper(__ct_rune_t _c)
 {
-	return (_c < 0 || _c >= __mb_sb_limit) ? _c :
+	int __limit;
+
+	(void) __runes_for_locale((locale_t)-2, &__limit);
+	return (_c < 0 || _c >= __limit) ? _c :
 	       _CurrentRuneLocale->__mapupper[_c];
 }
 
@@ -159,7 +172,10 @@
 static __inline __ct_rune_t
 __sbtolower(__ct_rune_t _c)
 {
-	return (_c < 0 || _c >= __mb_sb_limit) ? _c :
+	int __limit;
+
+	(void) __runes_for_locale((locale_t)-2, &__limit);
+	return (_c < 0 || _c >= __limit) ? _c :
 	       _CurrentRuneLocale->__maplower[_c];
 }
 
diff --git a/include/xlocale/_ctype.h b/include/xlocale/_ctype.h
--- a/include/xlocale/_ctype.h
+++ b/include/xlocale/_ctype.h
@@ -38,17 +38,11 @@
 #define _XLOCALE_CTYPE_H
 #endif
 
-#ifndef _LOCALE_T_DEFINED
-#define _LOCALE_T_DEFINED
-typedef struct	_xlocale *locale_t;
-#endif
-
 #ifndef _XLOCALE_RUN_FUNCTIONS_DEFINED
 #define _XLOCALE_RUN_FUNCTIONS_DEFINED 1
 unsigned long	 ___runetype_l(__ct_rune_t, locale_t) __pure;
 __ct_rune_t	 ___tolower_l(__ct_rune_t, locale_t) __pure;
 __ct_rune_t	 ___toupper_l(__ct_rune_t, locale_t) __pure;
-_RuneLocale	*__runes_for_locale(locale_t, int*);
 #endif
 
 #ifndef _XLOCALE_INLINE
diff --git a/lib/libc/locale/xlocale_private.h b/lib/libc/locale/xlocale_private.h
--- a/lib/libc/locale/xlocale_private.h
+++ b/lib/libc/locale/xlocale_private.h
@@ -208,7 +208,7 @@
 }
 
 /**
- * Two magic values are allowed for locale_t objects.  NULL and -1.  This
+ * Three magic values are allowed for locale_t objects.  NULL, -1, and -2.  This
  * function maps those to the real locales that they represent.
  */
 static inline locale_t get_real_locale(locale_t locale)
@@ -216,6 +216,7 @@
 	switch ((intptr_t)locale) {
 		case 0: return (&__xlocale_C_locale);
 		case -1: return (&__xlocale_global_locale);
+		case -2: return (__get_locale());
 		default: return (locale);
 	}
 }