diff --git a/include/battle.h b/include/battle.h
index 6c528866cf..3861aa8339 100755
--- a/include/battle.h
+++ b/include/battle.h
@@ -61,6 +61,7 @@ struct DisableStruct
 {
     u32 transformedMonPersonality;
     bool8 transformedMonShininess;
+    u16 transformedMonSpecies;
     u16 disabledMove;
     u16 encoredMove;
     u8 protectUses:4;
diff --git a/src/battle_script_commands.c b/src/battle_script_commands.c
index 4fd3c472e8..de8d68cb51 100644
--- a/src/battle_script_commands.c
+++ b/src/battle_script_commands.c
@@ -11310,6 +11310,7 @@ static void Cmd_transformdataexecution(void)
         gBattleMons[gBattlerAttacker].volatiles.transformed = TRUE;
         gDisableStructs[gBattlerAttacker].disabledMove = MOVE_NONE;
         gDisableStructs[gBattlerAttacker].disableTimer = 0;
+        gDisableStructs[gBattlerAttacker].transformedMonSpecies = gBattleMons[gBattlerAttacker].species;
         gDisableStructs[gBattlerAttacker].transformedMonPersonality = gBattleMons[gBattlerTarget].personality;
         if (B_TRANSFORM_SHINY >= GEN_4)
             gDisableStructs[gBattlerAttacker].transformedMonShininess = gBattleMons[gBattlerTarget].isShiny;
diff --git a/src/battle_util.c b/src/battle_util.c
index 9787bbe282..ee3ae241f7 100644
--- a/src/battle_util.c
+++ b/src/battle_util.c
@@ -8145,8 +8145,13 @@ static inline u32 CalcDefenseStat(struct DamageContext *ctx)
             modifier = uq4_12_multiply_half_down(modifier, UQ_4_12(2.0));
         break;
     case HOLD_EFFECT_EVIOLITE:
-        if (CanEvolve(gBattleMons[battlerDef].species))
-            modifier = uq4_12_multiply_half_down(modifier, UQ_4_12(1.5));
+        {
+            u16 species = gBattleMons[battlerDef].species;
+            if (gBattleMons[battlerDef].volatiles.transformed && gDisableStructs[battlerDef].transformedMonSpecies != SPECIES_NONE)
+                species = gDisableStructs[battlerDef].transformedMonSpecies;
+            if (CanEvolve(species))
+                modifier = uq4_12_multiply_half_down(modifier, UQ_4_12(1.5));
+        }
         break;
     case HOLD_EFFECT_ASSAULT_VEST:
         if (!usesDefStat)
diff --git a/test/battle/hold_effect/eviolite.c b/test/battle/hold_effect/eviolite.c
index 1aa0622e43..5387d50929 100644
--- a/test/battle/hold_effect/eviolite.c
+++ b/test/battle/hold_effect/eviolite.c
@@ -1,4 +1,82 @@
 #include "global.h"
 #include "test/battle.h"
 
-TO_DO_BATTLE_TEST("TODO: Write Eviolite (Hold Effect) test titles")
+ASSUMPTIONS
+{
+    ASSUME(gItemsInfo[ITEM_EVIOLITE].holdEffect == HOLD_EFFECT_EVIOLITE);
+}
+
+SINGLE_BATTLE_TEST("Eviolite boosts Defense and Sp. Def for unevolved Pokemon", s16 damage)
+{
+    u16 move;
+    u32 item;
+
+    PARAMETRIZE { move = MOVE_SCRATCH;   item = ITEM_EVIOLITE; }
+    PARAMETRIZE { move = MOVE_SCRATCH;   item = ITEM_NONE; }
+    PARAMETRIZE { move = MOVE_WATER_GUN; item = ITEM_EVIOLITE; }
+    PARAMETRIZE { move = MOVE_WATER_GUN; item = ITEM_NONE; }
+
+    GIVEN {
+        ASSUME(GetMoveCategory(MOVE_SCRATCH) == DAMAGE_CATEGORY_PHYSICAL);
+        ASSUME(GetMoveCategory(MOVE_WATER_GUN) == DAMAGE_CATEGORY_SPECIAL);
+        PLAYER(SPECIES_PIKACHU) { Item(item); }
+        OPPONENT(SPECIES_MAGIKARP) { Moves(MOVE_SCRATCH, MOVE_WATER_GUN); }
+    } WHEN {
+        TURN { MOVE(opponent, move); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, move, opponent);
+        HP_BAR(player, captureDamage: &results[i].damage);
+    } FINALLY {
+        EXPECT_MUL_EQ(results[0].damage, Q_4_12(1.5), results[1].damage);
+        EXPECT_MUL_EQ(results[2].damage, Q_4_12(1.5), results[3].damage);
+    }
+}
+
+SINGLE_BATTLE_TEST("Eviolite does not boost Defense or Sp. Def for evolved Pokemon", s16 damage)
+{
+    u16 move;
+    u32 item;
+
+    PARAMETRIZE { move = MOVE_SCRATCH;   item = ITEM_EVIOLITE; }
+    PARAMETRIZE { move = MOVE_SCRATCH;   item = ITEM_NONE; }
+    PARAMETRIZE { move = MOVE_WATER_GUN; item = ITEM_EVIOLITE; }
+    PARAMETRIZE { move = MOVE_WATER_GUN; item = ITEM_NONE; }
+
+    GIVEN {
+        ASSUME(GetMoveCategory(MOVE_SCRATCH) == DAMAGE_CATEGORY_PHYSICAL);
+        ASSUME(GetMoveCategory(MOVE_WATER_GUN) == DAMAGE_CATEGORY_SPECIAL);
+        PLAYER(SPECIES_RAICHU) { Item(item); }
+        OPPONENT(SPECIES_MAGIKARP) { Moves(MOVE_SCRATCH, MOVE_WATER_GUN); }
+    } WHEN {
+        TURN { MOVE(opponent, move); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, move, opponent);
+        HP_BAR(player, captureDamage: &results[i].damage);
+    } FINALLY {
+        EXPECT_MUL_EQ(results[0].damage, Q_4_12(1.0), results[1].damage);
+        EXPECT_MUL_EQ(results[2].damage, Q_4_12(1.0), results[3].damage);
+    }
+}
+
+SINGLE_BATTLE_TEST("Eviolite uses original species after Transform", s16 damage)
+{
+    u32 item;
+
+    PARAMETRIZE { item = ITEM_EVIOLITE; }
+    PARAMETRIZE { item = ITEM_NONE; }
+
+    GIVEN {
+        ASSUME(GetMoveEffect(MOVE_TRANSFORM) == EFFECT_TRANSFORM);
+        PLAYER(SPECIES_PIKACHU) { Item(item); Moves(MOVE_TRANSFORM, MOVE_CELEBRATE); }
+        OPPONENT(SPECIES_GYARADOS) { Moves(MOVE_SCRATCH, MOVE_CELEBRATE); }
+    } WHEN {
+        TURN { MOVE(player, MOVE_TRANSFORM); MOVE(opponent, MOVE_CELEBRATE); }
+        TURN { MOVE(player, MOVE_CELEBRATE); MOVE(opponent, MOVE_SCRATCH); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_TRANSFORM, player);
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_SCRATCH, opponent);
+        HP_BAR(player, captureDamage: &results[i].damage);
+    } FINALLY {
+        EXPECT_MUL_EQ(results[0].damage, Q_4_12(1.5), results[1].damage);
+    }
+}