diff --git a/src/drivers/rc/dsm_rc/DsmRc.cpp b/src/drivers/rc/dsm_rc/DsmRc.cpp
index 1b87a1ca92..af3a02bdb1 100644
--- a/src/drivers/rc/dsm_rc/DsmRc.cpp
+++ b/src/drivers/rc/dsm_rc/DsmRc.cpp
@@ -180,6 +180,10 @@ void DsmRc::Run()
 
 					} else if (dsm_bind_mode == vehicle_command_s::RC_SUB_TYPE_SPEKTRUM_DSMX8) {
 						dsm_bind_pulses = DSMX8_BIND_PULSES;
+
+					} else {
+						PX4_WARN("invalid Spektrum bind sub-type: %d", dsm_bind_mode);
+						cmd_ret = vehicle_command_ack_s::VEHICLE_CMD_RESULT_DENIED;
 					}
 
 					if (dsm_bind_pulses > 0 && bind_spektrum(dsm_bind_pulses)) {
diff --git a/src/drivers/rc_input/RCInput.cpp b/src/drivers/rc_input/RCInput.cpp
index b0ec0e7299..c65ac00817 100644
--- a/src/drivers/rc_input/RCInput.cpp
+++ b/src/drivers/rc_input/RCInput.cpp
@@ -402,6 +402,10 @@ void RCInput::Run()
 
 						} else if (dsm_bind_mode == vehicle_command_s::RC_SUB_TYPE_SPEKTRUM_DSMX8) {
 							dsm_bind_pulses = DSMX8_BIND_PULSES;
+
+						} else {
+							PX4_WARN("invalid Spektrum bind sub-type: %d", dsm_bind_mode);
+							cmd_ret = vehicle_command_ack_s::VEHICLE_CMD_RESULT_DENIED;
 						}
 
 						if (dsm_bind_pulses > 0 && bind_spektrum(dsm_bind_pulses)) {