diff --git a/ArduPlane/Parameters.pde b/ArduPlane/Parameters.pde
index 272212788c..dd5f7721ae 100644
--- a/ArduPlane/Parameters.pde
+++ b/ArduPlane/Parameters.pde
@@ -580,7 +580,7 @@ const AP_Param::Info var_info[] PROGMEM = {
 
     // @Param: ALT_HOLD_RTL
     // @DisplayName: RTL altitude
-    // @Description: Return to launch target altitude
+    // @Description: Return to launch target altitude. This is the altitude the plane will aim for and loiter at when returning home. If this is negative (usually -1) then the plane will use the current altitude at the time of entering RTL.
     // @Units: centimeters
     // @User: User
     GSCALAR(RTL_altitude_cm,        "ALT_HOLD_RTL",   ALT_HOLD_HOME_CM),