diff --git a/dcs/mission.py b/dcs/mission.py
index e237dfc5..e464d289 100644
--- a/dcs/mission.py
+++ b/dcs/mission.py
@@ -1022,6 +1022,10 @@ def _load_tasks(mp: MovingPoint, maintask: Type[task.MainTask]):
     def update_warehouses(self):
         """Some units need to have warehouse entries. This function updates warehouse entries based on units defined
         in the mission.
+
+        Gap-fill only: units that need a warehouse entry but do not have one get a default, while existing entries
+        are preserved. Without this guard the entries were overwritten with defaults on every save, discarding any
+        customized warehouse configuration for ships and FARPs.
         """
         coalition_to_warehouse_names = {'red': 'RED', 'blue': 'BLUE', 'neutrals': 'NEUTRAL'}
         for coalition_name in self.coalition:
@@ -1030,13 +1034,13 @@ def update_warehouses(self):
                 # Ships that can have aircraft parked need a warehouse entry.
                 for ship_group in self.coalition[coalition_name].countries[country_name].ship_group:
                     for unit_ in ship_group.units:
-                        if ships.ship_map[unit_.type].parking > 0:
+                        if ships.ship_map[unit_.type].parking > 0 and int(unit_.id) not in self.warehouses.warehouses:
                             self.warehouses.warehouses[int(unit_.id)] = terrain_.terrain.Warehouse().dict()
                             self.warehouses.warehouses[int(unit_.id)]['coalition'] = coalition_name_in_warehouse
                 # FARPs need a warehouse entry.
                 for static_group in self.coalition[coalition_name].countries[country_name].static_group:
                     for unit_ in static_group.units:
-                        if isinstance(unit_, unit.BaseFARP):
+                        if isinstance(unit_, unit.BaseFARP) and int(unit_.id) not in self.warehouses.warehouses:
                             self.warehouses.warehouses[int(unit_.id)] = terrain_.terrain.Warehouse().dict()
                             self.warehouses.warehouses[int(unit_.id)]['coalition'] = coalition_name_in_warehouse
 
diff --git a/tests/test_mission.py b/tests/test_mission.py
index 4c86900b..591f3344 100644
--- a/tests/test_mission.py
+++ b/tests/test_mission.py
@@ -1476,3 +1476,39 @@ def test_ground_control_password(self) -> None:
         self.assertIn(Coalition.Blue.value,
                       m2.groundControl.dict()["passwords"][GroundControlRole.OBSERVER.value])
         self.assertIn(Coalition.Red.value, m2.groundControl.dict()["passwords"][GroundControlRole.JTAC.value])
+
+
+class UpdateWarehousesTest(unittest.TestCase):
+
+    def _carrier_unit_id(self, m):
+        # A carrier is a ship whose type has parking > 0 -- exactly the unit
+        # class update_warehouses() creates warehouse entries for (FARPs are the
+        # other; the gap-fill logic is identical for both).
+        group = m.ship_group(
+            m.country("USA"), "CSG", dcs.ships.Stennis,
+            dcs.mapping.Point(-290000, 620000, m.terrain),
+        )
+        return int(group.units[0].id)
+
+    def test_update_warehouses_preserves_existing_entries(self):
+        # update_warehouses() runs on every Mission.save(). It must NOT overwrite
+        # an existing (possibly customized) ship/FARP warehouse entry with a fresh
+        # default; before the gap-fill guard, custom warehouse config was lost on
+        # every save.
+        m = dcs.mission.Mission(terrain=dcs.terrain.Caucasus())
+        uid = self._carrier_unit_id(m)
+
+        m.warehouses.warehouses[uid] = {"coalition": "BLUE", "size": 42}
+        m.update_warehouses()
+
+        self.assertEqual(m.warehouses.warehouses[uid]["size"], 42)
+        self.assertEqual(m.warehouses.warehouses[uid]["coalition"], "BLUE")
+
+    def test_update_warehouses_gap_fills_missing_entries(self):
+        # A unit that needs a warehouse but has none still gets a default entry.
+        m = dcs.mission.Mission(terrain=dcs.terrain.Caucasus())
+        uid = self._carrier_unit_id(m)
+
+        self.assertNotIn(uid, m.warehouses.warehouses)
+        m.update_warehouses()
+        self.assertIn(uid, m.warehouses.warehouses)