diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 8cc2f25d8a6a78b52afa98573b8806e81462a691..403d30e13bca346c9adbffcb0941e610e323ed47 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -701,8 +701,12 @@ bool hpage_1m_allowed(void)
 static char *machine_get_loadparm(Object *obj, Error **errp)
 {
     S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
+    char *loadparm_str;
 
-    return g_memdup(ms->loadparm, sizeof(ms->loadparm));
+    /* make a NUL-terminated string */
+    loadparm_str = g_memdup(ms->loadparm, sizeof(ms->loadparm) + 1);
+    loadparm_str[sizeof(ms->loadparm)] = 0;
+    return loadparm_str;
 }
 
 static void machine_set_loadparm(Object *obj, const char *val, Error **errp)