diff --git a/ArduCopter/mode_guided.cpp b/ArduCopter/mode_guided.cpp
index 7f3dec433f..8302e2668d 100644
--- a/ArduCopter/mode_guided.cpp
+++ b/ArduCopter/mode_guided.cpp
@@ -153,6 +153,9 @@ void ModeGuided::pva_control_start()
 
     // initialise yaw
     auto_yaw.set_mode_to_default(false);
+
+    // initialise terain alt
+    guided_pos_terrain_alt = false;
 }
 
 // initialise guided mode's position controller