diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 4365df3..39e3e8f 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -31,13 +31,10 @@
 #include <asm/div64.h>
 #include <asm/sections.h>	/* for dereference_function_descriptor() */
 
-/* Works only for digits and letters, but small and fast */
-#define TOLOWER(x) ((x) | 0x20)
-
 static unsigned int simple_guess_base(const char *cp)
 {
 	if (cp[0] == '0') {
-		if (TOLOWER(cp[1]) == 'x' && isxdigit(cp[2]))
+		if (_tolower(cp[1]) == 'x' && isxdigit(cp[2]))
 			return 16;
 		else
 			return 8;
@@ -59,13 +56,13 @@
 	if (!base)
 		base = simple_guess_base(cp);
 
-	if (base == 16 && cp[0] == '0' && TOLOWER(cp[1]) == 'x')
+	if (base == 16 && cp[0] == '0' && _tolower(cp[1]) == 'x')
 		cp += 2;
 
 	while (isxdigit(*cp)) {
 		unsigned int value;
 
-		value = isdigit(*cp) ? *cp - '0' : TOLOWER(*cp) - 'a' + 10;
+		value = isdigit(*cp) ? *cp - '0' : _tolower(*cp) - 'a' + 10;
 		if (value >= base)
 			break;
 		result = result * base + value;
@@ -1036,8 +1033,8 @@
 qualifier:
 	/* get the conversion qualifier */
 	spec->qualifier = -1;
-	if (*fmt == 'h' || TOLOWER(*fmt) == 'l' ||
-	    TOLOWER(*fmt) == 'z' || *fmt == 't') {
+	if (*fmt == 'h' || _tolower(*fmt) == 'l' ||
+	    _tolower(*fmt) == 'z' || *fmt == 't') {
 		spec->qualifier = *fmt++;
 		if (unlikely(spec->qualifier == *fmt)) {
 			if (spec->qualifier == 'l') {
@@ -1104,7 +1101,7 @@
 			spec->type = FORMAT_TYPE_LONG;
 		else
 			spec->type = FORMAT_TYPE_ULONG;
-	} else if (TOLOWER(spec->qualifier) == 'z') {
+	} else if (_tolower(spec->qualifier) == 'z') {
 		spec->type = FORMAT_TYPE_SIZE_T;
 	} else if (spec->qualifier == 't') {
 		spec->type = FORMAT_TYPE_PTRDIFF;
@@ -1263,7 +1260,7 @@
 			if (qualifier == 'l') {
 				long *ip = va_arg(args, long *);
 				*ip = (str - buf);
-			} else if (TOLOWER(qualifier) == 'z') {
+			} else if (_tolower(qualifier) == 'z') {
 				size_t *ip = va_arg(args, size_t *);
 				*ip = (str - buf);
 			} else {
@@ -1550,7 +1547,7 @@
 			void *skip_arg;
 			if (qualifier == 'l')
 				skip_arg = va_arg(args, long *);
-			else if (TOLOWER(qualifier) == 'z')
+			else if (_tolower(qualifier) == 'z')
 				skip_arg = va_arg(args, size_t *);
 			else
 				skip_arg = va_arg(args, int *);
@@ -1856,8 +1853,8 @@
 
 		/* get conversion qualifier */
 		qualifier = -1;
-		if (*fmt == 'h' || TOLOWER(*fmt) == 'l' ||
-		    TOLOWER(*fmt) == 'z') {
+		if (*fmt == 'h' || _tolower(*fmt) == 'l' ||
+		    _tolower(*fmt) == 'z') {
 			qualifier = *fmt++;
 			if (unlikely(qualifier == *fmt)) {
 				if (qualifier == 'h') {