diff --git a/sc2/bot_ai_internal.py b/sc2/bot_ai_internal.py
index 056fa2a6..8bf8fa9f 100644
--- a/sc2/bot_ai_internal.py
+++ b/sc2/bot_ai_internal.py
@@ -722,6 +722,7 @@ def _prepare_units(self: BotAI) -> None:
         self.reactor_tags: set[int] = set()
 
         worker_types: set[UnitTypeId] = {UnitTypeId.DRONE, UnitTypeId.DRONEBURROWED, UnitTypeId.SCV, UnitTypeId.PROBE}
+        structure_types: frozenset[int] = self.game_data.structure_types
 
         index: int = 0
         for unit in self.state.observation_raw.units:
@@ -760,7 +761,7 @@ def _prepare_units(self: BotAI) -> None:
                 elif alliance == 1:
                     self.all_own_units.append(unit_obj)
                     unit_id: UnitTypeId = unit_obj.type_id
-                    if unit_obj.is_structure:
+                    if unit_type in structure_types:
                         self.structures.append(unit_obj)
                         if unit_id in race_townhalls[self.race]:
                             self.townhalls.append(unit_obj)
@@ -790,7 +791,7 @@ def _prepare_units(self: BotAI) -> None:
                 # Alliance.Enemy.value = 4
                 elif alliance == 4:
                     self.all_enemy_units.append(unit_obj)
-                    if unit_obj.is_structure:
+                    if unit_type in structure_types:
                         self.enemy_structures.append(unit_obj)
                     else:
                         self.enemy_units.append(unit_obj)
diff --git a/sc2/game_data.py b/sc2/game_data.py
index 1a590952..c3acef62 100644
--- a/sc2/game_data.py
+++ b/sc2/game_data.py
@@ -30,6 +30,10 @@ def __init__(self, data: sc2api_pb2.ResponseData) -> None:
         }
         self.units: dict[int, UnitTypeData] = {u.unit_id: UnitTypeData(self, u) for u in data.units if u.available}
         self.upgrades: dict[int, UpgradeData] = {u.upgrade_id: UpgradeData(self, u) for u in data.upgrades}
+        # Precomputed structure type IDs (raw ints) for O(1) membership checks
+        self.structure_types: frozenset[int] = frozenset(
+            u.unit_id for u in data.units if u.available and Attribute.Structure.value in u.attributes
+        )
         # Cached UnitTypeIds so that conversion does not take long. This needs to be moved elsewhere if a new GameData object is created multiple times per game
 
     @lru_cache(maxsize=256)
diff --git a/sc2/unit.py b/sc2/unit.py
index 73c519b0..466db93c 100644
--- a/sc2/unit.py
+++ b/sc2/unit.py
@@ -34,7 +34,6 @@
     IS_RETURNING,
     IS_REVEALED,
     IS_SNAPSHOT,
-    IS_STRUCTURE,
     IS_VISIBLE,
     OFF_CREEP_SPEED_INCREASE_DICT,
     OFF_CREEP_SPEED_UPGRADE_DICT,
@@ -162,7 +161,7 @@ def tag(self) -> int:
     @property
     def is_structure(self) -> bool:
         """Checks if the unit is a structure."""
-        return IS_STRUCTURE in self._type_data._proto.attributes
+        return self._proto.unit_type in self._bot_object.game_data.structure_types
 
     @property
     def is_light(self) -> bool: