Index: stand/i386/boot2/boot2.c
===================================================================
--- stand/i386/boot2/boot2.c
+++ stand/i386/boot2/boot2.c
@@ -387,10 +387,11 @@
 #if SERIAL
 				} else if (c == 'S') {
 					j = 0;
-					while (*arg <= '9') {
-						i = (unsigned int)(*arg - '0');
+					i = (int)(*arg - '0');
+					while (i >= 0 && i <= 9) {
 						j = j * 10 + i;
 						arg++;
+						i = (int)(*arg - '0');
 					}
 					if (j > 0 && i == -'0') {
 						comspeed = j;