diff --git a/src/data/ability.ts b/src/data/ability.ts
index 64f48b08dc7..28cccd6f4ae 100644
--- a/src/data/ability.ts
+++ b/src/data/ability.ts
@@ -8,7 +8,7 @@ import { Weather, WeatherType } from "./weather";
 import { BattlerTag, GroundedTag, GulpMissileTag, SemiInvulnerableTag } from "./battler-tags";
 import { StatusEffect, getNonVolatileStatusEffects, getStatusEffectDescriptor, getStatusEffectHealText } from "./status-effect";
 import { Gender } from "./gender";
-import Move, { AttackMove, MoveCategory, MoveFlags, MoveTarget, FlinchAttr, OneHitKOAttr, HitHealAttr, allMoves, StatusMove, SelfStatusMove, VariablePowerAttr, applyMoveAttrs, IncrementMovePriorityAttr, VariableMoveTypeAttr, RandomMovesetMoveAttr, RandomMoveAttr, NaturePowerAttr, CopyMoveAttr, MoveAttr, MultiHitAttr, ChargeAttr, SacrificialAttr, SacrificialAttrOnHit, NeutralDamageAgainstFlyingTypeMultiplierAttr } from "./move";
+import Move, { AttackMove, MoveCategory, MoveFlags, MoveTarget, FlinchAttr, OneHitKOAttr, HitHealAttr, allMoves, StatusMove, SelfStatusMove, VariablePowerAttr, applyMoveAttrs, IncrementMovePriorityAttr, VariableMoveTypeAttr, RandomMovesetMoveAttr, RandomMoveAttr, NaturePowerAttr, CopyMoveAttr, MoveAttr, MultiHitAttr, ChargeAttr, SacrificialAttr, SacrificialAttrOnHit, NeutralDamageAgainstFlyingTypeMultiplierAttr, FixedDamageAttr } from "./move";
 import { ArenaTagSide, ArenaTrapTag } from "./arena-tag";
 import { Stat, getStatName } from "./pokemon-stat";
 import { BerryModifier, PokemonHeldItemModifier } from "../modifier/modifier";
@@ -481,12 +481,27 @@ export class NonSuperEffectiveImmunityAbAttr extends TypeImmunityAbAttr {
  * @extends PreDefendAbAttr
  */
 export class FullHpResistTypeAbAttr extends PreDefendAbAttr {
+  /**
+   * Reduces a type multiplier to 0.5 if the source is at full HP.
+   * @param pokemon {@linkcode Pokemon} the Pokemon with this ability
+   * @param passive n/a
+   * @param simulated n/a (this doesn't change game state)
+   * @param attacker n/a
+   * @param move {@linkcode Move} the move being used on the source
+   * @param cancelled n/a
+   * @param args `[0]` a container for the move's current type effectiveness multiplier
+   * @returns `true` if the move's effectiveness is reduced; `false` otherwise
+   */
   applyPreDefend(pokemon: Pokemon, passive: boolean, simulated: boolean, attacker: Pokemon, move: Move | null, cancelled: Utils.BooleanHolder | null, args: any[]): boolean | Promise<boolean> {
     const typeMultiplier = args[0];
     if (!(typeMultiplier && typeMultiplier instanceof Utils.NumberHolder)) {
       return false;
     }
 
+    if (move && move.hasAttr(FixedDamageAttr)) {
+      return false;
+    }
+
     if (pokemon.isFullHp() && typeMultiplier.value > 0.5) {
       typeMultiplier.value = 0.5;
       return true;
diff --git a/src/test/abilities/tera_shell.test.ts b/src/test/abilities/tera_shell.test.ts
index 050f9c756c2..4daeb866dfd 100644
--- a/src/test/abilities/tera_shell.test.ts
+++ b/src/test/abilities/tera_shell.test.ts
@@ -1,6 +1,7 @@
 import { Abilities } from "#app/enums/abilities";
 import { Moves } from "#app/enums/moves";
 import { Species } from "#app/enums/species";
+import { HitResult } from "#app/field/pokemon.js";
 import GameManager from "#test/utils/gameManager";
 import Phaser from "phaser";
 import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
@@ -89,4 +90,22 @@ describe("Abilities - Tera Shell", () => {
       expect(playerPokemon.getMoveEffectiveness).toHaveLastReturnedWith(0.25);
     }, TIMEOUT
   );
+
+  it(
+    "should not affect the effectiveness of fixed-damage moves",
+    async () => {
+      game.override.enemyMoveset(Array(4).fill(Moves.DRAGON_RAGE));
+
+      await game.startBattle([Species.SNORLAX]);
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      vi.spyOn(playerPokemon, "apply");
+
+      game.move.select(Moves.SPLASH);
+
+      await game.phaseInterceptor.to("BerryPhase", false);
+      expect(playerPokemon.apply).toHaveLastReturnedWith(HitResult.EFFECTIVE);
+      expect(playerPokemon.hp).toBe(playerPokemon.getMaxHp() - 40);
+    }, TIMEOUT
+  );
 });