diff --git a/Tools/AP_Periph/can.cpp b/Tools/AP_Periph/can.cpp
index 12a6d1445a..7442777d97 100644
--- a/Tools/AP_Periph/can.cpp
+++ b/Tools/AP_Periph/can.cpp
@@ -1956,6 +1956,10 @@ void AP_Periph_FW::can_gps_update(void)
         pkt.latitude_deg_1e8 = uint64_t(loc.lat) * 10ULL;
         pkt.height_ellipsoid_mm = loc.alt * 10;
         pkt.height_msl_mm = loc.alt * 10;
+        float undulation;
+        if (gps.get_undulation(undulation)) {
+            pkt.height_ellipsoid_mm -= undulation*1000;
+        }
         for (uint8_t i=0; i<3; i++) {
             pkt.ned_velocity[i] = vel[i];
         }