diff --git a/ArduPlane/AP_Arming.cpp b/ArduPlane/AP_Arming.cpp
index 057bec9238..dd86879c51 100644
--- a/ArduPlane/AP_Arming.cpp
+++ b/ArduPlane/AP_Arming.cpp
@@ -262,6 +262,10 @@ bool AP_Arming_Plane::disarm(const AP_Arming::Method method, bool do_disarm_chec
     }
 #endif
 
+    // re-initialize speed variable used in AUTO and GUIDED for
+    // DO_CHANGE_SPEED commands
+    plane.new_airspeed_cm = -1;
+    
     gcs().send_text(MAV_SEVERITY_INFO, "Throttle disarmed");
 
     return true;