diff --git a/flix/mavlink.ino b/flix/mavlink.ino
index be90f9a..6c15f1f 100644
--- a/flix/mavlink.ino
+++ b/flix/mavlink.ino
@@ -245,40 +245,44 @@ void handleMavlink(const void *_msg) {
 		}
 	}
 
-	// Handle commands
 	if (msg.msgid == MAVLINK_MSG_ID_COMMAND_LONG) {
 		mavlink_command_long_t m;
 		mavlink_msg_command_long_decode(&msg, &m);
 		if (m.target_system && m.target_system != mavlinkSysId) return;
-		mavlink_message_t response;
-		bool accepted = false;
 
-		if (m.command == MAV_CMD_REQUEST_MESSAGE && m.param1 == MAVLINK_MSG_ID_AUTOPILOT_VERSION) {
-			accepted = true;
-			mavlink_msg_autopilot_version_pack(mavlinkSysId, MAV_COMP_ID_AUTOPILOT1, &response,
-				MAV_PROTOCOL_CAPABILITY_PARAM_FLOAT | MAV_PROTOCOL_CAPABILITY_MAVLINK2, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0);
-			sendMessage(&response);
-		}
-
-		if (m.command == MAV_CMD_COMPONENT_ARM_DISARM) {
-			if (m.param1 == 1 && controlThrottle > 0.05) return; // don't arm if throttle is not low
-			accepted = true;
-			armed = m.param1 == 1;
-		}
-
-		if (m.command == MAV_CMD_DO_SET_MODE) {
-			if (m.param2 < 0 || m.param2 > AUTO) return; // incorrect mode
-			accepted = true;
-			mode = m.param2;
-		}
-
-		// send command ack
+		int result = handleMavlinkCommand(&m);
 		mavlink_message_t ack;
-		mavlink_msg_command_ack_pack(mavlinkSysId, MAV_COMP_ID_AUTOPILOT1, &ack, m.command, accepted ? MAV_RESULT_ACCEPTED : MAV_RESULT_UNSUPPORTED, UINT8_MAX, 0, msg.sysid, msg.compid);
+		mavlink_msg_command_ack_pack(mavlinkSysId, MAV_COMP_ID_AUTOPILOT1, &ack, m.command, result, UINT8_MAX, 0, msg.sysid, msg.compid);
 		sendMessage(&ack);
 	}
 }
 
+int handleMavlinkCommand(const void *_m) {
+	const mavlink_command_long_t& m = *(mavlink_command_long_t *)_m;
+
+	if (m.command == MAV_CMD_REQUEST_MESSAGE && m.param1 == MAVLINK_MSG_ID_AUTOPILOT_VERSION) {
+		mavlink_message_t response;
+		mavlink_msg_autopilot_version_pack(mavlinkSysId, MAV_COMP_ID_AUTOPILOT1, &response,
+			MAV_PROTOCOL_CAPABILITY_PARAM_FLOAT | MAV_PROTOCOL_CAPABILITY_MAVLINK2, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0);
+		sendMessage(&response);
+		return MAV_RESULT_ACCEPTED;
+	}
+
+	if (m.command == MAV_CMD_COMPONENT_ARM_DISARM) {
+		if (m.param1 == 1 && controlThrottle > 0.05) return MAV_RESULT_DENIED; // don't arm if throttle is not low
+		armed = m.param1 == 1;
+		return MAV_RESULT_ACCEPTED;
+	}
+
+	if (m.command == MAV_CMD_DO_SET_MODE) {
+		if (m.param2 < 0 || m.param2 > AUTO) return MAV_RESULT_DENIED; // incorrect mode
+		mode = m.param2;
+		return MAV_RESULT_ACCEPTED;
+	}
+
+	return MAV_RESULT_UNSUPPORTED;
+}
+
 // Send shell output to GCS
 void mavlinkPrint(const char* str) {
 	mavlinkPrintBuffer += str;
diff --git a/gazebo/flix.h b/gazebo/flix.h
index 351d371..d3034d2 100644
--- a/gazebo/flix.h
+++ b/gazebo/flix.h
@@ -58,6 +58,7 @@ void sendMavlink();
 void sendMessage(const void *msg);
 void receiveMavlink();
 void handleMavlink(const void *_msg);
+int handleMavlinkCommand(const void *_m);
 void mavlinkPrint(const char* str);
 void sendMavlinkPrint();
 inline Quaternion fluToFrd(const Quaternion &q);
diff --git a/tools/pyflix/__init__.py b/tools/pyflix/__init__.py
index 67ad6a7..411ab97 100644
--- a/tools/pyflix/__init__.py
+++ b/tools/pyflix/__init__.py
@@ -1 +1 @@
-from .flix import Flix
+from .flix import Flix, mavlink
diff --git a/tools/pyflix/flix.py b/tools/pyflix/flix.py
index c9b3b1d..8321d67 100644
--- a/tools/pyflix/flix.py
+++ b/tools/pyflix/flix.py
@@ -262,7 +262,9 @@ class Flix:
             try:
                 logger.debug(f'Send command {command} with params {params} (attempt #{attempt + 1})')
                 self.mavlink.command_long_send(self.system_id, 0, command, 0, *params)  # type: ignore
-                self.wait('mavlink.COMMAND_ACK', value=lambda msg: msg.command == command and msg.result == mavlink.MAV_RESULT_ACCEPTED, timeout=0.1)
+                ack = self.wait('mavlink.COMMAND_ACK', value=lambda msg: msg.command == command, timeout=0.1)
+                if ack.result != mavlink.MAV_RESULT_ACCEPTED:
+                    raise RuntimeError(f'Command {command} failed with result {ack.result}')
                 return
             except TimeoutError:
                 continue
diff --git a/tools/test.py b/tools/test.py
index c23e4c4..dca8046 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -2,10 +2,10 @@
 
 # Script for testing pyflix and the simulation.
 
-from pytest import approx
+from pytest import approx, raises
 from math import isnan, isfinite
 import time
-from pyflix import Flix
+from pyflix import Flix, mavlink
 
 def test():
     print('=== Connect...')
@@ -45,3 +45,6 @@ def test():
     flix.wait('mode', 'ACRO')
     flix.set_mode('AUTO')
     flix.wait('mode', 'AUTO')
+
+    raises(RuntimeError, lambda: flix._command_send(mavlink.MAV_CMD_DO_SET_MODE, [0, 99, 0, 0, 0, 0, 0]))  # invalid mode
+    raises(RuntimeError, lambda: flix._command_send(mavlink.MAV_CMD_DO_PARACHUTE, [0, 0, 0, 0, 0, 0, 0]))  # unsupported command