diff --git a/arch/util.h b/arch/util.h
index 08a7bb4..5a38c1a 100644
--- a/arch/util.h
+++ b/arch/util.h
@@ -35,7 +35,7 @@ void itoa(char *buf, int base, int d)
     // Divide UD by DIVISOR until UD == 0.
     do {
         int remainder = ud % divisor;
-        *p++ = (remainder < 10) ? remainder + '0' : remainder + 'a' - 10;
+        *p++ = (remainder < 10) ? remainder + '0' : remainder + 'A' - 10;
     }
     while (ud /= divisor);