diff --git a/variants/heltec_v3/platformio.ini b/variants/heltec_v3/platformio.ini
index 1715e36195..347cfb002b 100644
--- a/variants/heltec_v3/platformio.ini
+++ b/variants/heltec_v3/platformio.ini
@@ -109,6 +109,7 @@ lib_deps =
 [env:Heltec_v3_repeater_observer_mqtt]
 extends = Heltec_lora32_v3
 upload_port = /dev/cu.usbserial-4
+; External I2C sensors (BMP280 etc.) on header pins 33/34, same as the Heltec_v3_sensor env
 extra_scripts =
   ${esp32_base.extra_scripts}
   pre:scripts/generate_cert_bundle.py
@@ -142,6 +143,8 @@ build_flags =
 #  -D MQTT_PORT=1883
 #  -D MQTT_USERNAME='"your-username"'
 #  -D MQTT_PASSWORD='"your-password"'
+  -D ENV_PIN_SDA=33
+  -D ENV_PIN_SCL=34
 build_src_filter = ${Heltec_lora32_v3.build_src_filter}
   +<helpers/bridges/MQTTBridge.cpp>
   +<helpers/MQTTMessageBuilder.cpp>