diff --git a/variants/heltec_v3/platformio.ini b/variants/heltec_v3/platformio.ini
index 305d5782..039126bb 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
@@ -143,6 +144,8 @@ 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>
@@ -191,6 +194,7 @@ lib_deps =
 
 [env:Heltec_v3_room_server_observer_mqtt]
 extends = Heltec_lora32_v3
+; 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
@@ -217,6 +221,8 @@ build_flags =
   -D ESP32_CPU_FREQ=160
   -D MQTT_WIFI_TX_POWER=WIFI_POWER_11dBm
   -D WITH_SNMP=1
+  -D ENV_PIN_SDA=33
+  -D ENV_PIN_SCL=34
 build_src_filter = ${Heltec_lora32_v3.build_src_filter}
   +<helpers/ui/SSD1306Display.cpp>
   +<helpers/bridges/MQTTBridge.cpp>
diff --git a/variants/rak3112/platformio.ini b/variants/rak3112/platformio.ini
index 6cc8b914..36432af4 100644
--- a/variants/rak3112/platformio.ini
+++ b/variants/rak3112/platformio.ini
@@ -100,6 +100,7 @@ lib_deps =
 
 [env:RAK_3112_repeater_observer_mqtt]
 extends = rak3112
+; External I2C sensors on pins 33/34, same as the RAK_3112_sensor env
 extra_scripts =
   ${esp32_base.extra_scripts}
   pre:scripts/generate_cert_bundle.py
@@ -130,6 +131,8 @@ 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 = ${rak3112.build_src_filter}
   +<helpers/bridges/MQTTBridge.cpp>
   +<helpers/MQTTMessageBuilder.cpp>
@@ -165,6 +168,7 @@ lib_deps =
 
 [env:RAK_3112_room_server_observer_mqtt]
 extends = rak3112
+; External I2C sensors on pins 33/34, same as the RAK_3112_sensor env
 extra_scripts =
   ${esp32_base.extra_scripts}
   pre:scripts/generate_cert_bundle.py
@@ -190,6 +194,8 @@ build_flags =
   -D ESP32_CPU_FREQ=160
   -D MQTT_WIFI_TX_POWER=WIFI_POWER_11dBm
   -D WITH_SNMP=1
+  -D ENV_PIN_SDA=33
+  -D ENV_PIN_SCL=34
 build_src_filter = ${rak3112.build_src_filter}
   +<helpers/bridges/MQTTBridge.cpp>
   +<helpers/MQTTMessageBuilder.cpp>