diff --git a/stand/i386/gptboot/gptboot.c b/stand/i386/gptboot/gptboot.c
index 68ef55073ecb..7b5423ede6d8 100644
--- a/stand/i386/gptboot/gptboot.c
+++ b/stand/i386/gptboot/gptboot.c
@@ -574,10 +574,12 @@ parse_cmds(char *cmdstr, int *dskupdated)
 				if (arg[1] != 'p' || gdsk.dsk.unit > 9)
 					return (-1);
 				arg += 2;
-				gdsk.dsk.part = *arg - '0';
-				if (gdsk.dsk.part < 1 || gdsk.dsk.part > 9)
+				j = 0;
+				while (*arg >= '0' && *arg <= '9')
+					j = j * 10 + *arg++ - '0';
+				gdsk.dsk.part = j;
+				if (gdsk.dsk.part < 1 || gdsk.dsk.part > 128)
 					return (-1);
-				arg++;
 				if (arg[0] != ')')
 					return (-1);
 				arg++;