diff --git a/message_definitions/v1.0/common.xml b/message_definitions/v1.0/common.xml
index 87dde9eb98..23aefda1ec 100644
--- a/message_definitions/v1.0/common.xml
+++ b/message_definitions/v1.0/common.xml
@@ -2252,7 +2252,7 @@
                <field type="uint8_t" name="target">The system to be controlled.</field>
                <field type="int16_t" name="x">X-axis, normalized to the range [-1000,1000]. A value of INT16_MAX indicates that this axis is invalid. Generally corresponds to forward(1000)-backward(-1000) movement on a joystick and the pitch of a vehicle.</field>
                <field type="int16_t" name="y">Y-axis, normalized to the range [-1000,1000]. A value of INT16_MAX indicates that this axis is invalid. Generally corresponds to left(-1000)-right(1000) movement on a joystick and the roll of a vehicle.</field>
-               <field type="int16_t" name="z">Z-axis, normalized to the range [-1000,1000]. A value of INT16_MAX indicates that this axis is invalid. Generally corresponds to a separate slider movement with maximum being 1000 and minimum being -1000 on a joystick and the thrust of a vehicle.</field>
+               <field type="int16_t" name="z">Z-axis, normalized to the range [-1000,1000]. A value of INT16_MAX indicates that this axis is invalid. Generally corresponds to a separate slider movement with maximum being 1000 and minimum being -1000 on a joystick and the thrust of a vehicle. Positive values are forward thrust, negative values are reverse thrust.</field>
                <field type="int16_t" name="r">R-axis, normalized to the range [-1000,1000]. A value of INT16_MAX indicates that this axis is invalid. Generally corresponds to a twisting of the joystick, with counter-clockwise being 1000 and clockwise being -1000, and the yaw of a vehicle.</field>
                <field type="uint16_t" name="buttons">A bitfield corresponding to the joystick buttons' current state, 1 for pressed, 0 for released. The lowest bit corresponds to Button 1.</field>
           </message>