diff --git a/src/typval.c b/src/typval.c
index 35c9e24..af96b31 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -2425,7 +2425,7 @@
 			  if (vim_isxdigit(p[1]))
 			  {
 			      int	n, nr;
-			      int	c = toupper(*p);
+			      int	c = SAFE_toupper(*p);
 
 			      if (c == 'X')
 				  n = 2;