diff --git a/src/battle_main.c b/src/battle_main.c
index 67f2cf1737..99ab2a87a1 100644
--- a/src/battle_main.c
+++ b/src/battle_main.c
@@ -4914,6 +4914,7 @@ static void TurnValuesCleanUp(bool8 var0)
         else
         {
             memset(&gProtectStructs[i], 0, sizeof(struct ProtectStruct));
+            memset(&gQueuedStatBoosts[i], 0, sizeof(gQueuedStatBoosts));
 
             if (gDisableStructs[i].isFirstTurn)
                 gDisableStructs[i].isFirstTurn--;
diff --git a/test/battle/ability/opportunist.c b/test/battle/ability/opportunist.c
index 79c6649f59..60e127c708 100644
--- a/test/battle/ability/opportunist.c
+++ b/test/battle/ability/opportunist.c
@@ -101,6 +101,24 @@ DOUBLE_BATTLE_TEST("Opportunist raises Attack only once when partner has Intimid
     }
 }
 
+SINGLE_BATTLE_TEST("Opportunist does not accumulate opposing mon's stat changes")
+{
+    GIVEN {
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_ESPATHRA) { Ability(ABILITY_OPPORTUNIST); }
+    } WHEN {
+        TURN { MOVE(player, MOVE_SWORDS_DANCE); }
+        TURN { MOVE(player, MOVE_SWORDS_DANCE); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_SWORDS_DANCE, player);
+        ABILITY_POPUP(opponent, ABILITY_OPPORTUNIST);
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_SWORDS_DANCE, player);
+        ABILITY_POPUP(opponent, ABILITY_OPPORTUNIST);
+    } THEN {
+        EXPECT_EQ(opponent->statStages[STAT_ATK], DEFAULT_STAT_STAGE + 4);
+    }
+}
+
 TO_DO_BATTLE_TEST("Opportunist doesn't copy ally stat increases");
 TO_DO_BATTLE_TEST("Opportunist doesn't copy foe stat increases gained via Opportunist");
 TO_DO_BATTLE_TEST("Opportunist copies foe stat increased gained via Swagger and Flatter");