diff --git a/libraries/SITL/SIM_RF_NMEA.h b/libraries/SITL/SIM_RF_NMEA.h
index 7a667a7fdc..d9dbb8079b 100644
--- a/libraries/SITL/SIM_RF_NMEA.h
+++ b/libraries/SITL/SIM_RF_NMEA.h
@@ -18,6 +18,7 @@
 ./Tools/autotest/sim_vehicle.py --gdb --debug -v ArduCopter -A --uartF=sim:nmea --speedup=1
 
 param set SERIAL5_PROTOCOL 9
+param set SERIAL5_BAUD 9600
 param set RNGFND1_TYPE 17
 graph RANGEFINDER.distance
 graph GLOBAL_POSITION_INT.relative_alt/1000-RANGEFINDER.distance
@@ -36,6 +37,8 @@ namespace SITL {
 class RF_NMEA : public SerialRangeFinder {
 public:
 
+    uint32_t device_baud() const override { return 9600; }
+
     uint32_t packet_for_alt(uint16_t alt_cm, uint8_t *buffer, uint8_t buflen) override;
 
     bool has_temperature() const override { return true; }
diff --git a/libraries/SITL/SIM_SerialDevice.cpp b/libraries/SITL/SIM_SerialDevice.cpp
index cf442083dc..d4f798aabf 100644
--- a/libraries/SITL/SIM_SerialDevice.cpp
+++ b/libraries/SITL/SIM_SerialDevice.cpp
@@ -64,6 +64,10 @@ ssize_t SerialDevice::read_from_autopilot(char *buffer, const size_t size) const
 
 ssize_t SerialDevice::write_to_autopilot(const char *buffer, const size_t size) const
 {
+    if (device_baud() != 0 && autopilot_baud != 0 && device_baud() != autopilot_baud) {
+        return -1;
+    }
+
     const ssize_t ret = to_autopilot->write((uint8_t*)buffer, size);
     // ::fprintf(stderr, "write to autopilot: (");
     // for (ssize_t i=0; i<ret; i++) {
@@ -79,6 +83,10 @@ ssize_t SerialDevice::write_to_autopilot(const char *buffer, const size_t size)
 
 ssize_t SerialDevice::read_from_device(char *buffer, const size_t size) const
 {
+    if (device_baud() != 0 && autopilot_baud != 0 && device_baud() != autopilot_baud) {
+        return -1;
+    }
+
     const ssize_t ret = to_autopilot->read((uint8_t*)buffer, size);
     return ret;
 }
diff --git a/libraries/SITL/SIM_SerialDevice.h b/libraries/SITL/SIM_SerialDevice.h
index cdfe5637f2..6dba244061 100644
--- a/libraries/SITL/SIM_SerialDevice.h
+++ b/libraries/SITL/SIM_SerialDevice.h
@@ -32,10 +32,12 @@ public:
     // methods for autopilot to use to talk to device:
     ssize_t read_from_device(char *buffer, size_t size) const;
     ssize_t write_to_device(const char *buffer, size_t size) const;
+    void set_autopilot_baud(uint32_t baud) { autopilot_baud = baud; }
 
     // methods for simulated device to use:
     ssize_t read_from_autopilot(char *buffer, size_t size) const;
     virtual ssize_t write_to_autopilot(const char *buffer, size_t size) const;
+    virtual uint32_t device_baud() const { return 0; }  // 0 meaning unset
 
 protected:
 
@@ -45,6 +47,10 @@ protected:
     ByteBuffer *from_autopilot;
 
     bool init_sitl_pointer();
+
+private:
+
+    uint32_t autopilot_baud;
 };
 
 }