diff --git a/examples/device/dfu_freertos/src/usb_descriptors.c b/examples/device/dfu_freertos/src/usb_descriptors.c
index 496bc8dc7..d4ecc2840 100644
--- a/examples/device/dfu_freertos/src/usb_descriptors.c
+++ b/examples/device/dfu_freertos/src/usb_descriptors.c
@@ -146,6 +146,14 @@ uint16_t const* tud_descriptor_string_cb(uint8_t index, uint16_t langid)
 
     if ( !(index < sizeof(string_desc_arr)/sizeof(string_desc_arr[0])) ) return NULL; // check if requested descriptor exists
     const char* str = string_desc_arr[index]; // load requested string
+    if (3 == index) { // serial
+        // set MAC as serial
+        uint8_t mac[6];
+        esp_read_mac(mac, ESP_MAC_ETH);
+        char usb_serial[13] = {0};
+        snprintf(usb_serial, sizeof(usb_serial), "%02X%02X%02X%02X%02X%02X", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
+        str = usb_serial;
+    }
 
     // check string length
     chr_count = strlen(str);