diff --git a/wiflash_esp32/wiflash_esp32.ino b/wiflash_esp32/wiflash_esp32.ino
index e50a13d..93f0c30 100644
--- a/wiflash_esp32/wiflash_esp32.ino
+++ b/wiflash_esp32/wiflash_esp32.ino
@@ -102,6 +102,7 @@ uint32_t change_time;    // time of button press (ms)
 */
 void setup() {
   Serial.begin(115200);
+  while (!Serial); // wait for serial attach
 
   Serial.println("Disabling Bluetooth.");
   btStop();