diff --git a/src/stlink-lib/usb.c b/src/stlink-lib/usb.c
index e37b531e..b6195aad 100644
--- a/src/stlink-lib/usb.c
+++ b/src/stlink-lib/usb.c
@@ -1117,7 +1117,7 @@ uint32_t stlink_serial(struct libusb_device_handle *handle, struct libusb_device
 		return 0;
 	}
 
-	return strlen(serial);
+	return (uint32_t)strlen(serial);
 }
 
 /**