diff --git a/conf/messages.xml b/conf/messages.xml
index 834e395f3c..770ecdaf70 100644
--- a/conf/messages.xml
+++ b/conf/messages.xml
@@ -356,7 +356,7 @@
     <field name="wp_id" type="uint8"/>
     <field name="lat" type="int32" unit="1e7deg" alt_unit="deg" alt_unit_coef="0.0000001"/>
     <field name="lon" type="int32" unit="1e7deg" alt_unit="deg" alt_unit_coef="0.0000001"/>
-    <field name="alt" type="int32" unit="cm"/>
+    <field name="alt" type="int32" unit="mm" alt_unit="m">Height above Mean Sea Level (geoid)</field>
   </message>
 
   <message name="CHRONO" id="48">
@@ -2223,7 +2223,7 @@
   <field name="ac_id" type="uint8"/>
   <field name="lat" type="int32" unit="1e7deg" alt_unit="deg" alt_unit_coef="0.0000001"/>
   <field name="lon" type="int32" unit="1e7deg" alt_unit="deg" alt_unit_coef="0.0000001"/>
-  <field name="alt" type="int32" unit="cm"/>
+  <field name="alt" type="int32" unit="cm" alt_unit="m">Height above Mean Sea Level (geoid)</field>
  </message>
 
  <message name="WIND_INFO" id="3" link="forwarded">
diff --git a/sw/ground_segment/tmtc/fw_server.ml b/sw/ground_segment/tmtc/fw_server.ml
index 756acea4bb..f9bd8c9b9f 100644
--- a/sw/ground_segment/tmtc/fw_server.ml
+++ b/sw/ground_segment/tmtc/fw_server.ml
@@ -318,7 +318,7 @@ let log_and_parse = fun ac_name (a:Aircraft.aircraft) msg values ->
       and lon = ivalue "lon"
       and alt = ivalue "alt" in
       let geo = make_geo_deg (float lat /. 1e7) (float lon /. 1e7) in
-      update_waypoint a (ivalue "wp_id") geo (float alt /. 100.)
+      update_waypoint a (ivalue "wp_id") geo (float alt /. 1000.)
     | "GENERIC_COM" ->
       let flight_time = ivalue "flight_time" in
       if flight_time >= a.flight_time then begin