--- include/SDL_stdinc.h	2006-06-27 06:48:32.000000000 +0200
+++ include/SDL_stdinc.h	2006-10-07 01:52:02.000000000 +0200
@@ -217,10 +217,10 @@
 #define SDL_max(x, y)	(((x) > (y)) ? (x) : (y))
 
 #ifdef HAVE_CTYPE_H
-#define SDL_isdigit(X)  isdigit(X)
-#define SDL_isspace(X)  isspace(X)
-#define SDL_toupper(X)  toupper(X)
-#define SDL_tolower(X)  tolower(X)
+#define SDL_isdigit(X)  isdigit((unsigned char)(X))
+#define SDL_isspace(X)  isspace((unsigned char)(X))
+#define SDL_toupper(X)  toupper((unsigned char)(X))
+#define SDL_tolower(X)  tolower((unsigned char)(X))
 #else
 #define SDL_isdigit(X)  (((X) >= '0') && ((X) <= '9'))
 #define SDL_isspace(X)  (((X) == ' ') || ((X) == '\t') || ((X) == '\r') || ((X) == '\n'))