diff --git a/Tools/autotest/arduplane.py b/Tools/autotest/arduplane.py
index 4d0d7b50cf..fc81448ad1 100644
--- a/Tools/autotest/arduplane.py
+++ b/Tools/autotest/arduplane.py
@@ -2753,15 +2753,26 @@ class AutoTestPlane(AutoTest):
         self.progress("loitering at %um" % alt)
         tstart = self.get_sim_time()
         timeout = 60*15  # enough time to do one and a bit circles
+        max_delta = 0
         while True:
             now = self.get_sim_time_cached()
             if now - tstart > timeout:
                 break
+            gpi = self.assert_receive_message('GLOBAL_POSITION_INT')
             terrain = self.assert_receive_message('TERRAIN_REPORT')
             rel_alt = terrain.current_height
-            self.progress("%um above terrain" % rel_alt)
+            self.progress("%um above terrain (%um bove home)" %
+                          (rel_alt, gpi.relative_alt/1000.0))
             if rel_alt > alt*1.2 or rel_alt < alt * 0.8:
                 raise NotAchievedException("Not terrain following")
+            delta = abs(rel_alt - gpi.relative_alt/1000.0)
+            if delta > max_delta:
+                max_delta = delta
+        want_max_delta = 30
+        if max_delta < want_max_delta:
+            raise NotAchievedException(
+                "Expected terrain and home alts to vary more than they did (max=%u want=%u)" %
+                (max_delta, want_max_delta))
         self.context_pop()
         self.progress("Returning home")
         self.fly_home_land_and_disarm(240)