diff --git a/sim/pokemon.ts b/sim/pokemon.ts
index dbffa6995071..6b6503ac6317 100644
--- a/sim/pokemon.ts
+++ b/sim/pokemon.ts
@@ -1222,8 +1222,9 @@ export class Pokemon {
 		const species = pokemon.species;
 		if (pokemon.fainted || this.illusion || pokemon.illusion || (pokemon.volatiles['substitute'] && this.battle.gen >= 5) ||
 			(pokemon.transformed && this.battle.gen >= 2) || (this.transformed && this.battle.gen >= 5) ||
-			species.name === 'Eternatus-Eternamax' || (['Ogerpon', 'Terapagos'].includes(species.baseSpecies) &&
-			(this.terastallized || pokemon.terastallized)) || this.terastallized === 'Stellar') {
+			species.name === 'Eternatus-Eternamax' || ['Ogerpon', 'Terapagos'].includes(this.species.baseSpecies) ||
+			(['Ogerpon', 'Terapagos'].includes(species.baseSpecies) && (this.terastallized || pokemon.terastallized)) ||
+			this.terastallized === 'Stellar') {
 			return false;
 		}
 
diff --git a/test/sim/abilities/terashell.js b/test/sim/abilities/terashell.js
index 6625ffee518c..585077dc133c 100644
--- a/test/sim/abilities/terashell.js
+++ b/test/sim/abilities/terashell.js
@@ -64,18 +64,6 @@ describe('Tera Shell', function () {
 	});
 
 	it(`should not work if the user's species is not currently Terapagos-Terastal`, function () {
-		battle = common.createBattle([[
-			{species: 'Terapagos', ability: 'terashift', moves: ['transform']},
-		], [
-			{species: 'Umbreon', ability: 'terashell', moves: ['flowertrick']},
-		]]);
-
-		battle.makeChoices();
-		const terapagos = battle.p1.active[0];
-		let damage = terapagos.maxhp - terapagos.hp;
-		assert.bounded(damage, [51, 60], `Tera Shell should not have activated because current species is not Terapagos`);
-
-
 		battle = common.createBattle([[
 			{species: 'Espeon', moves: ['transform']},
 		], [
@@ -84,7 +72,7 @@ describe('Tera Shell', function () {
 
 		battle.makeChoices();
 		const espeon = battle.p1.active[0];
-		damage = espeon.maxhp - espeon.hp;
+		const damage = espeon.maxhp - espeon.hp;
 		assert.bounded(damage, [33, 39], `Tera Shell should have activated because current species is Terapagos`);
 	});
 
diff --git a/test/sim/misc/terapagos.js b/test/sim/misc/terapagos.js
index a1276f21a290..2ba840da7b96 100644
--- a/test/sim/misc/terapagos.js
+++ b/test/sim/misc/terapagos.js
@@ -24,19 +24,13 @@ describe(`Terapagos`, function () {
 		assert.false(!!ditto.terastallized);
 	});
 
-	it(`[Hackmons] should not cause Terapagos-Terastal to become Terapagos-Stellar if the user is Transformed`, function () {
+	it(`[Hackmons] can't use Transform`, function () {
 		battle = common.createBattle([[
-			{species: 'terapagos', ability: 'terashift', moves: ['transform'], teraType: 'Stellar'},
-			{species: 'pikachu', moves: ['sleeptalk']},
+			{species: 'terapagos', ability: 'terashift', moves: ['transform']},
 		], [
 			{species: 'silicobra', moves: ['sleeptalk']},
 		]]);
-
 		battle.makeChoices();
-		battle.makeChoices('move sleeptalk terastallize', 'auto');
-		battle.makeChoices('switch 2', 'auto');
-		battle.makeChoices('switch 2', 'auto');
-		const terapagos = battle.p1.active[0];
-		assert.species(terapagos, 'Terapagos-Terastal');
+		assert.species(battle.p1.active[0], 'Terapagos-Terastal');
 	});
 });