diff --git a/monitor.c b/monitor.c
index c2c1e42..8baeaf0 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2799,6 +2799,7 @@
             break;
         case 'o':
             {
+                int ret;
                 int64_t val;
                 char *end;
 
@@ -2811,8 +2812,8 @@
                         break;
                     }
                 }
-                val = qemu_strtosz_MiB(p, &end);
-                if (val < 0) {
+                ret = qemu_strtosz_MiB(p, &end, &val);
+                if (ret < 0) {
                     monitor_printf(mon, "invalid size\n");
                     goto fail;
                 }