diff --git a/vl.c b/vl.c
index f5afed4c49030f4dcad4755a7596719f83ff0d99..b9146cfdea1671655bfa25d0e8c1c3ce1487ba72 100644
--- a/vl.c
+++ b/vl.c
@@ -953,8 +953,8 @@ static void numa_add(const char *optarg)
             node_mem[nodenr] = 0;
         } else {
             int64_t sval;
-            sval = strtosz(option, NULL);
-            if (sval < 0) {
+            sval = strtosz(option, &endptr);
+            if (sval < 0 || *endptr) {
                 fprintf(stderr, "qemu: invalid numa mem size: %s\n", optarg);
                 exit(1);
             }