diff --git a/nuttx-patches/fix_CRTSCTS-define.patch b/nuttx-patches/fix_CRTSCTS-define.patch
new file mode 100644
index 0000000000..2c173118f6
--- /dev/null
+++ b/nuttx-patches/fix_CRTSCTS-define.patch
@@ -0,0 +1,12 @@
+diff -ruN NuttX/nuttx/include/termios.h NuttX/nuttx/include/termios.h
+--- NuttX/nuttx/include/termios.h	1969-12-31 14:00:00.000000000 -1000
++++ NuttX/nuttx/include/termios.h	2014-12-25 17:33:53.404950574 -1000
+@@ -110,8 +110,8 @@
+ #define HUPCL     (1 << 6)  /* Bit 6: Hang up on last close */
+ #define CLOCAL    (1 << 7)  /* Bit 7: Ignore modem status lines */
+ #define CCTS_OFLOW (1 << 8) /* Bit 8: CTS flow control of output */
+-#define CRTSCTS   CCTS_OFLOW
+ #define CRTS_IFLOW (1 << 9) /* Bit 9: RTS flow control of input */
++#define CRTSCTS   (CRTS_IFLOW | CCTS_OFLOW)
+ 
+ /* Local Modes (c_lflag in the termios structure) */
diff --git a/src/modules/mavlink/mavlink_main.cpp b/src/modules/mavlink/mavlink_main.cpp
index f4473bbcf6..03a68b2f82 100644
--- a/src/modules/mavlink/mavlink_main.cpp
+++ b/src/modules/mavlink/mavlink_main.cpp
@@ -87,10 +87,16 @@
 #include "mavlink_receiver.h"
 #include "mavlink_rate_limiter.h"
 
+// Guard against MAVLink misconfiguration
 #ifndef MAVLINK_CRC_EXTRA
 #error MAVLINK_CRC_EXTRA has to be defined on PX4 systems
 #endif
 
+// Guard against flow control misconfiguration
+#if defined (CRTSCTS) && defined (__PX4_NUTTX) && (CRTSCTS != (CRTS_IFLOW | CCTS_OFLOW))
+#error The non-standard CRTSCTS define is incorrect. Fix this in the OS or replace with (CRTS_IFLOW | CCTS_OFLOW)
+#endif
+
 #define DEFAULT_REMOTE_PORT_UDP			14550 ///< GCS port per MAVLink spec
 #define DEFAULT_DEVICE_NAME			"/dev/ttyS1"
 #define MAX_DATA_RATE				10000000	///< max data rate in bytes/s
@@ -705,10 +711,12 @@ int Mavlink::mavlink_open_uart(int baud, const char *uart_name)
 	case 1000000: speed = B1000000; break;
 
 #ifdef B1500000
+
 	case 1500000: speed = B1500000; break;
 #endif
 
 #ifdef B3000000
+
 	case 3000000: speed = B3000000; break;
 #endif
 
@@ -839,18 +847,11 @@ Mavlink::enable_flow_control(bool enabled)
 	int ret = tcgetattr(_uart_fd, &uart_config);
 
 	if (enabled) {
-#ifdef CRTS_IFLOW
-		uart_config.c_cflag |= CRTS_IFLOW;
-#else
 		uart_config.c_cflag |= CRTSCTS;
-#endif
 
 	} else {
-#ifdef CRTS_IFLOW
-		uart_config.c_cflag &= ~CRTS_IFLOW;
-#else
 		uart_config.c_cflag &= ~CRTSCTS;
-#endif
+
 	}
 
 	ret = tcsetattr(_uart_fd, TCSANOW, &uart_config);
@@ -1630,6 +1631,7 @@ Mavlink::update_rate_mult()
 	}
 
 	float mavlink_ulog_streaming_rate_inv = 1.0f;
+
 	if (_mavlink_ulog) {
 		mavlink_ulog_streaming_rate_inv = 1.f - _mavlink_ulog->current_data_rate();
 	}
@@ -2202,6 +2204,7 @@ Mavlink::task_main(int argc, char *argv[])
 
 		/* send command ACK */
 		uint16_t current_command_ack = 0;
+
 		if (ack_sub->update(&ack_time, &command_ack)) {
 			mavlink_command_ack_t msg;
 			msg.result = command_ack.result;
@@ -2234,15 +2237,19 @@ Mavlink::task_main(int argc, char *argv[])
 				_mavlink_ulog->stop();
 				_mavlink_ulog = nullptr;
 				_mavlink_ulog_stop_requested = false;
+
 			} else {
 				if (current_command_ack == vehicle_command_s::VEHICLE_CMD_LOGGING_START) {
 					_mavlink_ulog->start_ack_received();
 				}
+
 				int ret = _mavlink_ulog->handle_update(get_channel());
+
 				if (ret < 0) { //abort the streaming on error
 					if (ret != -1) {
 						PX4_WARN("mavlink ulog stream update failed, stopping (%i)", ret);
 					}
+
 					_mavlink_ulog->stop();
 					_mavlink_ulog = nullptr;
 				}
@@ -2534,14 +2541,17 @@ Mavlink::display_status()
 	printf("\ttxerr: %.3f kB/s\n", (double)_rate_txerr);
 	printf("\trx: %.3f kB/s\n", (double)_rate_rx);
 	printf("\trate mult: %.3f\n", (double)_rate_mult);
+
 	if (_mavlink_ulog) {
-		printf("\tULog rate: %.1f%% of max %.1f%%\n", (double)_mavlink_ulog->current_data_rate()*100.,
-				(double)_mavlink_ulog->maximum_data_rate()*100.);
+		printf("\tULog rate: %.1f%% of max %.1f%%\n", (double)_mavlink_ulog->current_data_rate() * 100.,
+		       (double)_mavlink_ulog->maximum_data_rate() * 100.);
 	}
+
 	printf("\taccepting commands: %s\n", (accepting_commands()) ? "YES" : "NO");
 	printf("\tMAVLink version: %i\n", _protocol_version);
 
 	printf("\ttransport protocol: ");
+
 	switch (_protocol) {
 	case UDP:
 		printf("UDP (%i)\n", _network_port);