diff --git a/src/xxd/xxd.c b/src/xxd/xxd.c
index c90bc02..26f8d83 100644
--- a/src/xxd/xxd.c
+++ b/src/xxd/xxd.c
@@ -96,8 +96,8 @@
 # include <unistd.h>
 #endif
 #include <stdlib.h>
-#include <string.h>	/* for strncmp() */
-#include <ctype.h>	/* for isalnum() */
+#include <string.h>
+#include <ctype.h>
 #include <limits.h>
 #if __MWERKS__ && !defined(BEBOX)
 # include <unix.h>	/* for fdopen() on MAC */
@@ -208,7 +208,7 @@
 #define HEX_BITS 3		/* not hex a dump, but bits: 01111001 */
 #define HEX_LITTLEENDIAN 4
 
-#define CONDITIONAL_CAPITALIZE(c) (capitalize ? toupper((int)c) : c)
+#define CONDITIONAL_CAPITALIZE(c) (capitalize ? toupper((unsigned char)(c)) : (c))
 
 #define COLOR_PROLOGUE \
 l[c++] = '\033'; \
@@ -952,9 +952,9 @@
 
       if (varname != NULL)
 	{
-	  FPRINTF_OR_DIE((fpo, "unsigned char %s", isdigit((int)varname[0]) ? "__" : ""));
+	  FPRINTF_OR_DIE((fpo, "unsigned char %s", isdigit((unsigned char)varname[0]) ? "__" : ""));
 	  for (e = 0; (c = varname[e]) != 0; e++)
-	    putc_or_die(isalnum(c) ? CONDITIONAL_CAPITALIZE(c) : '_', fpo);
+	    putc_or_die(isalnum((unsigned char)c) ? CONDITIONAL_CAPITALIZE(c) : '_', fpo);
 	  fputs_or_die("[] = {\n", fpo);
 	}
 
@@ -972,9 +972,9 @@
       if (varname != NULL)
 	{
 	  fputs_or_die("};\n", fpo);
-	  FPRINTF_OR_DIE((fpo, "unsigned int %s", isdigit((int)varname[0]) ? "__" : ""));
+	  FPRINTF_OR_DIE((fpo, "unsigned int %s", isdigit((unsigned char)varname[0]) ? "__" : ""));
 	  for (e = 0; (c = varname[e]) != 0; e++)
-	    putc_or_die(isalnum(c) ? CONDITIONAL_CAPITALIZE(c) : '_', fpo);
+	    putc_or_die(isalnum((unsigned char)c) ? CONDITIONAL_CAPITALIZE(c) : '_', fpo);
 	  FPRINTF_OR_DIE((fpo, "_%s = %d;\n", capitalize ? "LEN" : "len", p));
 	}