1 files changed, 4 insertions, 3 deletions
diff --git a/src/libstddjb/case_upperb.c b/src/libstddjb/case_upperb.c
index 78ece8f..f245f4d 100644
--- a/src/libstddjb/case_upperb.c
+++ b/src/libstddjb/case_upperb.c
@@ -1,13 +1,14 @@
 /* ISC license. */
 
+#include <ctype.h>
+
 #include <skalibs/bytestr.h>
 
 void case_upperb (char *s, size_t len)
 {
-  unsigned char const d = 'a' - 'A' ;
   while (len--)
   {
-    if (('a' <= *s) && (*s <= 'z')) *s -= d ;
-    ++s ;
+    int c = toupper(*s) ;
+    *s++ = (unsigned char)c ;
   }
 }