diff --git a/firmware/hackrf_usb/hackrf_usb.c b/firmware/hackrf_usb/hackrf_usb.c
index 4eddcae9..e842d82b 100644
--- a/firmware/hackrf_usb/hackrf_usb.c
+++ b/firmware/hackrf_usb/hackrf_usb.c
@@ -195,10 +195,11 @@ void usb_set_descriptor_by_serial_number(void)
 	iap_cmd_call(&iap_cmd_res);
 	
 	if (iap_cmd_res.status_res.status_ret == CMD_SUCCESS) {
-		usb_descriptor_string_serial_number[0] = 66;
+		usb_descriptor_string_serial_number[0] = USB_DESCRIPTOR_STRING_SERIAL_BUF_LEN;
 		usb_descriptor_string_serial_number[1] = USB_DESCRIPTOR_TYPE_STRING;
 		
-		for (size_t i=0; i<32; i++) {
+		/* 32 characters of serial number, convert to UTF-16LE */
+		for (size_t i=0; i<USB_DESCRIPTOR_STRING_SERIAL_LEN; i++) {
 			const uint_fast8_t nibble = (iap_cmd_res.status_res.iap_result[i >> 3] >> (28 - (i & 7) * 4)) & 0xf;
 			const char c = (nibble > 9) ? ('a' + nibble - 10) : ('0' + nibble);
 			usb_descriptor_string_serial_number[2 + i * 2] = c;
diff --git a/firmware/hackrf_usb/usb_descriptor.c b/firmware/hackrf_usb/usb_descriptor.c
index bc07c6e4..ff770b24 100644
--- a/firmware/hackrf_usb/usb_descriptor.c
+++ b/firmware/hackrf_usb/usb_descriptor.c
@@ -22,6 +22,7 @@
 #include <stdint.h>
 
 #include "usb_type.h"
+#include "usb_descriptor.h"
 
 #define USB_VENDOR_ID			(0x1D50)
 
@@ -329,9 +330,9 @@ uint8_t usb_descriptor_string_config2_description[] = {
 	'e', 0x00,
 };
 
-uint8_t usb_descriptor_string_serial_number[66];
+uint8_t usb_descriptor_string_serial_number[USB_DESCRIPTOR_STRING_SERIAL_BUF_LEN];
 
-uint8_t* const usb_descriptor_strings[] = {
+uint8_t* usb_descriptor_strings[] = {
 	usb_descriptor_string_languages,
 	usb_descriptor_string_manufacturer,
 	usb_descriptor_string_product,
diff --git a/firmware/hackrf_usb/usb_descriptor.h b/firmware/hackrf_usb/usb_descriptor.h
index 11e274a7..bffa9bf7 100644
--- a/firmware/hackrf_usb/usb_descriptor.h
+++ b/firmware/hackrf_usb/usb_descriptor.h
@@ -30,6 +30,9 @@ extern uint8_t usb_descriptor_configuration_cpld_update_high_speed[];
 extern uint8_t usb_descriptor_string_languages[];
 extern uint8_t usb_descriptor_string_manufacturer[];
 extern uint8_t usb_descriptor_string_product[];
+
+#define USB_DESCRIPTOR_STRING_SERIAL_LEN 32
+#define USB_DESCRIPTOR_STRING_SERIAL_BUF_LEN (USB_DESCRIPTOR_STRING_SERIAL_LEN*2 + 2) /* UTF-16LE */
 extern uint8_t usb_descriptor_string_serial_number[];
 
 extern uint8_t* usb_descriptor_strings[];