diff --git a/libraries/GCS_MAVLink/GCS_MAVLink.cpp b/libraries/GCS_MAVLink/GCS_MAVLink.cpp
index b2aad1120c..4bfb6b5f0a 100644
--- a/libraries/GCS_MAVLink/GCS_MAVLink.cpp
+++ b/libraries/GCS_MAVLink/GCS_MAVLink.cpp
@@ -32,6 +32,9 @@ This provides some support code and variables for MAVLink enabled sketches
 
 AP_HAL::BetterStream	*mavlink_comm_0_port;
 AP_HAL::BetterStream	*mavlink_comm_1_port;
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+AP_HAL::BetterStream	*mavlink_comm_2_port;
+#endif
 
 mavlink_system_t mavlink_system = {7,1,0,0};
 
@@ -73,6 +76,11 @@ void comm_send_buffer(mavlink_channel_t chan, const uint8_t *buf, uint8_t len)
 	case MAVLINK_COMM_1:
 		mavlink_comm_1_port->write(buf, len);
 		break;
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+	case MAVLINK_COMM_2:
+		mavlink_comm_2_port->write(buf, len);
+		break;
+#endif
 	default:
 		break;
 	}
diff --git a/libraries/GCS_MAVLink/GCS_MAVLink.h b/libraries/GCS_MAVLink/GCS_MAVLink.h
index 7956229ef8..72e51cc730 100644
--- a/libraries/GCS_MAVLink/GCS_MAVLink.h
+++ b/libraries/GCS_MAVLink/GCS_MAVLink.h
@@ -23,6 +23,11 @@
 #if CONFIG_HAL_BOARD == HAL_BOARD_APM1 || CONFIG_HAL_BOARD == HAL_BOARD_APM2
 #include <util/crc16.h>
 #define HAVE_CRC_ACCUMULATE
+// only two telemetry ports on APM1/APM2
+#define MAVLINK_COMM_NUM_BUFFERS 2
+#else
+// allow three telemetry ports on other boards
+#define MAVLINK_COMM_NUM_BUFFERS 3
 #endif
 
 #include "include/mavlink/v1.0/ardupilotmega/version.h"
@@ -32,15 +37,19 @@
 // those for APM
 #define MAVLINK_MAX_PAYLOAD_LEN 104
 
-#define MAVLINK_COMM_NUM_BUFFERS 2
 #include "include/mavlink/v1.0/mavlink_types.h"
 
-/// MAVLink stream used for HIL interaction
+/// MAVLink stream used for uartA
 extern AP_HAL::BetterStream	*mavlink_comm_0_port;
 
-/// MAVLink stream used for ground control communication
+/// MAVLink stream used for uartC
 extern AP_HAL::BetterStream	*mavlink_comm_1_port;
 
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+/// MAVLink stream used for uartD
+extern AP_HAL::BetterStream	*mavlink_comm_2_port;
+#endif
+
 /// MAVLink system definition
 extern mavlink_system_t mavlink_system;
 
@@ -58,6 +67,11 @@ static inline void comm_send_ch(mavlink_channel_t chan, uint8_t ch)
 	case MAVLINK_COMM_1:
 		mavlink_comm_1_port->write(ch);
 		break;
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+	case MAVLINK_COMM_2:
+		mavlink_comm_2_port->write(ch);
+		break;
+#endif
 	default:
 		break;
 	}
@@ -81,6 +95,11 @@ static inline uint8_t comm_receive_ch(mavlink_channel_t chan)
 	case MAVLINK_COMM_1:
 		data = mavlink_comm_1_port->read();
 		break;
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+	case MAVLINK_COMM_2:
+		data = mavlink_comm_2_port->read();
+		break;
+#endif
 	default:
 		break;
 	}
@@ -101,6 +120,11 @@ static inline uint16_t comm_get_available(mavlink_channel_t chan)
 	case MAVLINK_COMM_1:
 		bytes = mavlink_comm_1_port->available();
 		break;
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+	case MAVLINK_COMM_2:
+		bytes = mavlink_comm_2_port->available();
+		break;
+#endif
 	default:
 		break;
 	}
@@ -125,6 +149,11 @@ static inline uint16_t comm_get_txspace(mavlink_channel_t chan)
 	case MAVLINK_COMM_1:
 		ret = mavlink_comm_1_port->txspace();
 		break;
+#if MAVLINK_COMM_NUM_BUFFERS > 2
+	case MAVLINK_COMM_2:
+		ret = mavlink_comm_2_port->txspace();
+		break;
+#endif
 	default:
 		break;
 	}