diff --git a/ChangeLog b/ChangeLog
index 1ef4ff9e..0cba4da4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2016-04-18  Joerg Wunsch <j.gnu@uriah.heep.sax.de>
+
+	* usb_hidapi.c (usbhid_open): Correctly calculate the
+	offset for serial number matching
+
 2016-03-28  Joerg Wunsch <j.gnu@uriah.heep.sax.de>
 
 	bug #47550: Linux GPIO broken
diff --git a/usb_hidapi.c b/usb_hidapi.c
index 6af5dd53..81e9c4ab 100644
--- a/usb_hidapi.c
+++ b/usb_hidapi.c
@@ -108,7 +108,9 @@ static int usbhid_open(char * port, union pinfo pinfo, union filedescriptor *fd)
       {
 	avrdude_message(MSG_NOTICE, "%s: usbhid_open(): Found %ls, serno: %ls\n",
 			progname, walk->product_string, walk->serial_number);
-	if (wcscmp(walk->serial_number + serlen, wserno) == 0)
+	size_t slen = wcslen(walk->serial_number);
+	if (slen >= serlen &&
+	    wcscmp(walk->serial_number + slen - serlen, wserno) == 0)
           {
 	    /* found matching serial number */
 	    break;