diff --git a/hw/usb.c b/hw/usb.c
index b2830c59003e56f7791a02ee3ce80ae35b976682..758b341ff0f4908d32d9ebdb2ec06463e0a333ab 100644
--- a/hw/usb.c
+++ b/hw/usb.c
@@ -183,7 +183,7 @@ int set_usb_string(uint8_t *buf, const char *str)
 
     q = buf;
     len = strlen(str);
-    *q++ = 2 * len + 1;
+    *q++ = 2 * len + 2;
     *q++ = 3;
     for(i = 0; i < len; i++) {
         *q++ = str[i];