diff --git a/src/cjson.c b/src/cjson.c
index 807bd54..977fd3c 100644
--- a/src/cjson.c
+++ b/src/cjson.c
@@ -58,10 +58,10 @@ static int cJSON_strcasecmp( const char *s1, const char *s2 )
 		return ( s1 == s2 ) ? 0 : 1;
 	if ( ! s2 )
 		return 1;
-	for ( ; tolower(*s1) == tolower(*s2); ++s1, ++s2)
+	for ( ; tolower((u_char)*s1) == tolower((u_char)*s2); ++s1, ++s2)
 		if( *s1 == 0 )
 			return 0;
-	return tolower(*(const unsigned char *)s1) - tolower(*(const unsigned char *)s2);
+	return tolower((u_char)*s1) - tolower((u_char)*s2);
 }