diff --git a/src/data/egg.ts b/src/data/egg.ts
index 3bfd39382b5..eba3bab0d87 100644
--- a/src/data/egg.ts
+++ b/src/data/egg.ts
@@ -140,8 +140,9 @@ export class Egg {
   constructor(eggOptions?: IEggOptions) {
     //if (eggOptions.tier && eggOptions.species) throw Error("Error egg can't have species and tier as option. only choose one of them.")
 
-    this._tier = eggOptions.tier ?? (Overrides.EGG_TIER_OVERRIDE ?? this.rollEggTier());
     this._sourceType = eggOptions.sourceType ?? undefined;
+    // Ensure _sourceType is defined before invoking rollEggTier(), as it is referenced
+    this._tier = eggOptions.tier ?? (Overrides.EGG_TIER_OVERRIDE ?? this.rollEggTier());
     // If egg was pulled, check if egg pity needs to override the egg tier
     if (eggOptions.pulled) {
       // Needs this._tier and this._sourceType to work
diff --git a/src/test/eggs/egg.test.ts b/src/test/eggs/egg.test.ts
index 07678e7e1ea..a098620f5eb 100644
--- a/src/test/eggs/egg.test.ts
+++ b/src/test/eggs/egg.test.ts
@@ -1,4 +1,4 @@
-import {afterEach, beforeAll, beforeEach, describe, expect, it} from "vitest";
+import {afterEach, beforeAll, beforeEach, describe, expect, it, vi} from "vitest";
 import BattleScene from "../../battle-scene";
 import { Egg, getLegendaryGachaSpeciesForTimestamp } from "#app/data/egg.js";
 import { Species } from "#enums/species";
@@ -8,6 +8,7 @@ import { EggTier } from "#app/enums/egg-type.js";
 import { VariantTier } from "#app/enums/variant-tiers.js";
 import GameManager from "../utils/gameManager";
 import EggData from "#app/system/egg-data.js";
+import * as Utils from "#app/utils.js";
 
 describe("Egg Generation Tests", () => {
   let phaserGame: Phaser.Game;
@@ -21,6 +22,7 @@ describe("Egg Generation Tests", () => {
 
   afterEach(() => {
     game.phaseInterceptor.restoreOg();
+    vi.restoreAllMocks();
   });
 
   beforeEach(async() => {
@@ -288,4 +290,17 @@ describe("Egg Generation Tests", () => {
 
     expect(scene.gameData.gameStats.legendaryEggsPulled).toBe(startingLegendaryEggsPulled + 1);
   });
+  it("should increase legendary egg rate", () => {
+    vi.spyOn(Utils, "randInt").mockReturnValue(1);
+
+    const scene = game.scene;
+    const expectedTier1 = EggTier.MASTER;
+    const expectedTier2 = EggTier.ULTRA;
+
+    const result1 = new Egg({scene, sourceType: EggSourceType.GACHA_LEGENDARY, pulled: true}).tier;
+    const result2 = new Egg({scene, sourceType: EggSourceType.GACHA_MOVE, pulled: true}).tier;
+
+    expect(result1).toBe(expectedTier1);
+    expect(result2).toBe(expectedTier2);
+  });
 });