diff --git a/apollo/__tests__/Skill.test.tsx b/apollo/__tests__/Skill.test.tsx
index b46528b0..cbc9d37f 100644
--- a/apollo/__tests__/Skill.test.tsx
+++ b/apollo/__tests__/Skill.test.tsx
@@ -10,9 +10,11 @@ import {
   Saboteur,
   SmallTank,
   Sniper,
+  SuperTank,
   Zombie,
 } from '@deities/athena/info/Unit.tsx';
 import { generateUnitName } from '@deities/athena/info/UnitNames.tsx';
+import getDefenseStatusEffect from '@deities/athena/lib/getDefenseStatusEffect.tsx';
 import updatePlayer from '@deities/athena/lib/updatePlayer.tsx';
 import withModifiers from '@deities/athena/lib/withModifiers.tsx';
 import { Charge, MaxCharges } from '@deities/athena/map/Configuration.tsx';
@@ -682,3 +684,21 @@ test('the Charge skill increases charge accumulation', async () => {
     state1.getPlayer(1).charge,
   );
 });
+
+test('defense cannot go negative', async () => {
+  const skills = new Set([
+    Skill.DecreaseUnitCostAttackAndDefenseDecreaseMinor,
+    Skill.BuyUnitZombieDefenseDecreaseMajor,
+    Skill.UnlockZombie,
+  ]);
+  const mapA = map.copy({
+    teams: updatePlayer(map.teams, map.getPlayer(1).copy({ skills })),
+    units: map.units
+      .set(fromA, SuperTank.create(1))
+      .set(toA, SmallTank.create(2)),
+  });
+
+  expect(
+    getDefenseStatusEffect(mapA, mapA.units.get(fromA)!, null),
+  ).toBeGreaterThanOrEqual(0);
+});
diff --git a/athena/lib/getAttackStatusEffect.tsx b/athena/lib/getAttackStatusEffect.tsx
index 51e5c509..c21f3fd9 100644
--- a/athena/lib/getAttackStatusEffect.tsx
+++ b/athena/lib/getAttackStatusEffect.tsx
@@ -43,12 +43,13 @@ export default function getAttackStatusEffect(
       ? CrystalAttackEffect
       : 0;
 
-  return (
+  return Math.max(
+    0,
     1 +
-    crystalEffect +
-    buildingEffect +
-    unitEffect +
-    (unit.isLeader() ? LeaderStatusEffect : 0) +
-    getSkillAttackStatusEffects(unit, tile, player)
+      crystalEffect +
+      buildingEffect +
+      unitEffect +
+      (unit.isLeader() ? LeaderStatusEffect : 0) +
+      getSkillAttackStatusEffects(unit, tile, player),
   );
 }
diff --git a/athena/lib/getDefenseStatusEffect.tsx b/athena/lib/getDefenseStatusEffect.tsx
index a2c8459c..382018c7 100644
--- a/athena/lib/getDefenseStatusEffect.tsx
+++ b/athena/lib/getDefenseStatusEffect.tsx
@@ -10,14 +10,15 @@ export default function getDefenseStatusEffect(
   tile: TileInfo | null,
 ) {
   const player = map.getPlayer(entity);
-  return (
+  return Math.max(
+    0,
     1 +
-    (isUnit(entity) && entity.isLeader() ? LeaderStatusEffect : 0) +
-    getSkillDefenseStatusEffects(
-      entity,
-      tile,
-      player.skills,
-      player.activeSkills,
-    )
+      (isUnit(entity) && entity.isLeader() ? LeaderStatusEffect : 0) +
+      getSkillDefenseStatusEffects(
+        entity,
+        tile,
+        player.skills,
+        player.activeSkills,
+      ),
   );
 }