diff --git a/src/helpers/bridges/MQTTBridge.h b/src/helpers/bridges/MQTTBridge.h
index f6d54a10..e3f79dcc 100644
--- a/src/helpers/bridges/MQTTBridge.h
+++ b/src/helpers/bridges/MQTTBridge.h
@@ -11,8 +11,11 @@
 
 #if defined(MQTT_DEBUG) && defined(ARDUINO)
   #include <Arduino.h>
-  #define MQTT_DEBUG_PRINT(F, ...) Serial.printf("MQTT: " F, ##__VA_ARGS__)
-  #define MQTT_DEBUG_PRINTLN(F, ...) Serial.printf("MQTT: " F "\n", ##__VA_ARGS__)
+  // USB CDC-aware debug macros: only print if Serial is ready (non-blocking check)
+  // Serial.availableForWrite() returns bytes available in write buffer (>0 means ready)
+  // This prevents hangs when USB CDC isn't ready yet (e.g., ESP32-S3 native USB)
+  #define MQTT_DEBUG_PRINT(F, ...) do { if (Serial.availableForWrite() > 0) { Serial.printf("MQTT: " F, ##__VA_ARGS__); } } while(0)
+  #define MQTT_DEBUG_PRINTLN(F, ...) do { if (Serial.availableForWrite() > 0) { Serial.printf("MQTT: " F "\n", ##__VA_ARGS__); } } while(0)
 #else
   #define MQTT_DEBUG_PRINT(...) {}
   #define MQTT_DEBUG_PRINTLN(...) {}