diff --git a/vl.c b/vl.c
index b9146cf..a50842b 100644
--- a/vl.c
+++ b/vl.c
@@ -2535,9 +2535,10 @@
                 break;
             case QEMU_OPTION_m: {
                 int64_t value;
+                char *end;
 
-                value = strtosz(optarg, NULL);
-                if (value < 0) {
+                value = strtosz(optarg, &end);
+                if (value < 0 || *end) {
                     fprintf(stderr, "qemu: invalid ram size: %s\n", optarg);
                     exit(1);
                 }