diff --git a/os/various/chprintf.c b/os/various/chprintf.c
index 0c8cbb255..0b9ff2da5 100644
--- a/os/various/chprintf.c
+++ b/os/various/chprintf.c
@@ -229,9 +229,9 @@ void chprintf(BaseSequentialStream *chp, const char *fmt, ...) {
       c = 8;
 unsigned_common:
       if (is_long)
-        l = va_arg(ap, long);
+        l = va_arg(ap, unsigned long);
       else
-        l = va_arg(ap, int);
+        l = va_arg(ap, unsigned int);
       p = ltoa(p, l, c);
       break;
     default: