diff --git a/packages/core/src/DiscountTypes/BuyXGetY.php b/packages/core/src/DiscountTypes/BuyXGetY.php
index 8f53db4c38..840b32203c 100644
--- a/packages/core/src/DiscountTypes/BuyXGetY.php
+++ b/packages/core/src/DiscountTypes/BuyXGetY.php
@@ -249,18 +249,44 @@ private function processAutomaticRewards(CartContract $cart, int $remainingRewar
 
         // we have lines to add
         if ($remainingRewardQty > 0) {
-            while ($remainingRewardQty > 0) {
-                $selectedRewardItem = $this->discount->discountableRewards->random()->discountable;
+            // Fulfillable products per collection reward, hydrated once here rather
+            // than re-queried on every iteration of the allocation loop below.
+            $fulfillableCollectionProducts = [];
 
-                if (! $selectedRewardItem) {
-                    $remainingRewardQty--;
+            $fulfillableRewards = $this->discount->discountableRewards->filter(function ($discountableReward) use (&$fulfillableCollectionProducts) {
+                $rewardItem = $discountableReward->discountable;
 
-                    continue;
+                if (! $rewardItem) {
+                    return false;
+                }
+
+                if ($rewardItem instanceof LunarCollection) {
+                    $fulfillableCollectionProducts[$rewardItem->id] = $rewardItem->products()
+                        ->with('variants')
+                        ->get()
+                        ->filter(fn ($p) => $p->variants->first()?->canBeFulfilledAtQuantity(1))
+                        ->values();
+
+                    return $fulfillableCollectionProducts[$rewardItem->id]->isNotEmpty();
+                }
+
+                if ($rewardItem instanceof Purchasable) {
+                    return $rewardItem->canBeFulfilledAtQuantity(1);
                 }
 
+                return (bool) $rewardItem->variants->first()?->canBeFulfilledAtQuantity(1);
+            });
+
+            if ($fulfillableRewards->isEmpty()) {
+                return [$affectedLines, $discountTotal];
+            }
+
+            while ($remainingRewardQty > 0) {
+                $selectedRewardItem = $fulfillableRewards->random()->discountable;
+
                 if ($selectedRewardItem instanceof LunarCollection) {
-                    $product = $selectedRewardItem->products()->inRandomOrder()->first();
-                    $purchasable = $product?->variants()->first();
+                    $product = $fulfillableCollectionProducts[$selectedRewardItem->id]->random();
+                    $purchasable = $product->variants->first();
                     $selectedRewardItem = $product;
                 } elseif ($selectedRewardItem instanceof Purchasable) {
                     $purchasable = $selectedRewardItem;
@@ -276,6 +302,17 @@ private function processAutomaticRewards(CartContract $cart, int $remainingRewar
 
                 $rewardKey = $purchasable->getMorphClass().':'.$purchasable->id;
 
+                // How many units of this reward this run has already allocated,
+                // since canBeFulfilledAtQuantity below must check against that
+                // running total rather than a fixed quantity of 1 each time.
+                $allocated = $addedRewardLines[$rewardKey]->quantity ?? 0;
+
+                if (! $purchasable->canBeFulfilledAtQuantity($allocated + 1)) {
+                    $remainingRewardQty--;
+
+                    continue;
+                }
+
                 // is it already in cart?
                 $rewardLine = $addedRewardLines[$rewardKey] ?? $cart->lines->first(function ($line) use ($purchasable) {
                     return $line->purchasable->id == $purchasable->id;
diff --git a/tests/core/Unit/DiscountTypes/BuyXGetYTest.php b/tests/core/Unit/DiscountTypes/BuyXGetYTest.php
index a8cc12dd6d..96e2245ef2 100644
--- a/tests/core/Unit/DiscountTypes/BuyXGetYTest.php
+++ b/tests/core/Unit/DiscountTypes/BuyXGetYTest.php
@@ -1736,6 +1736,311 @@
     expect($rewardLine->purchasable_type)->toEqual($purchasableB->getMorphClass());
 });
 
+test('does not automatically add reward when product variant has no stock', function () {
+    $customerGroup = CustomerGroup::factory()->create(['default' => true]);
+    $channel = Channel::factory()->create(['default' => true]);
+    $currency = Currency::factory()->create(['code' => 'GBP']);
+
+    $productA = Product::factory()->create();
+    $productB = Product::factory()->create();
+
+    $purchasableA = ProductVariant::factory()->create(['product_id' => $productA->id]);
+    $purchasableB = ProductVariant::factory()->create([
+        'product_id' => $productB->id,
+        'purchasable' => 'in_stock',
+        'stock' => 0,
+    ]);
+
+    $cart = Cart::factory()->create([
+        'channel_id' => $channel->id,
+        'currency_id' => $currency->id,
+    ]);
+
+    foreach ([$purchasableA, $purchasableB] as $purchasable) {
+        Price::factory()->create([
+            'price' => 1000,
+            'min_quantity' => 1,
+            'currency_id' => $currency->id,
+            'priceable_type' => $purchasable->getMorphClass(),
+            'priceable_id' => $purchasable->id,
+        ]);
+    }
+
+    $cart->lines()->create([
+        'purchasable_type' => $purchasableA->getMorphClass(),
+        'purchasable_id' => $purchasableA->id,
+        'quantity' => 1,
+    ]);
+
+    $discount = Discount::factory()->create([
+        'type' => BuyXGetY::class,
+        'name' => 'Test Automatic Reward Out Of Stock',
+        'data' => [
+            'min_qty' => 1,
+            'reward_qty' => 1,
+            'automatically_add_rewards' => true,
+        ],
+    ]);
+
+    $discount->customerGroups()->sync([
+        $customerGroup->id => ['enabled' => true, 'starts_at' => now()],
+    ]);
+
+    $discount->channels()->sync([
+        $channel->id => ['enabled' => true, 'starts_at' => now()->subHour()],
+    ]);
+
+    $discount->discountableConditions()->create([
+        'discountable_type' => $productA->getMorphClass(),
+        'discountable_id' => $productA->id,
+    ]);
+
+    $discount->discountableRewards()->create([
+        'discountable_type' => $productB->getMorphClass(),
+        'discountable_id' => $productB->id,
+        'type' => 'reward',
+    ]);
+
+    $cart = $cart->calculate();
+
+    expect($cart->freeItems)->toBeNull();
+});
+
+test('does not automatically add collection reward when all products are out of stock', function () {
+    $customerGroup = CustomerGroup::factory()->create(['default' => true]);
+    $channel = Channel::factory()->create(['default' => true]);
+    $currency = Currency::factory()->create(['code' => 'GBP']);
+
+    $collection = Collection::factory()->create();
+
+    $productA = Product::factory()->create();
+    $productB = Product::factory()->create();
+
+    $productB->collections()->sync($collection);
+
+    $purchasableA = ProductVariant::factory()->create(['product_id' => $productA->id]);
+    $purchasableB = ProductVariant::factory()->create([
+        'product_id' => $productB->id,
+        'purchasable' => 'in_stock',
+        'stock' => 0,
+    ]);
+
+    $cart = Cart::factory()->create([
+        'channel_id' => $channel->id,
+        'currency_id' => $currency->id,
+    ]);
+
+    foreach ([$purchasableA, $purchasableB] as $purchasable) {
+        Price::factory()->create([
+            'price' => 1000,
+            'min_quantity' => 1,
+            'currency_id' => $currency->id,
+            'priceable_type' => $purchasable->getMorphClass(),
+            'priceable_id' => $purchasable->id,
+        ]);
+    }
+
+    $cart->lines()->create([
+        'purchasable_type' => $purchasableA->getMorphClass(),
+        'purchasable_id' => $purchasableA->id,
+        'quantity' => 1,
+    ]);
+
+    $discount = Discount::factory()->create([
+        'type' => BuyXGetY::class,
+        'name' => 'Test Automatic Collection Reward Out Of Stock',
+        'data' => [
+            'min_qty' => 1,
+            'reward_qty' => 1,
+            'automatically_add_rewards' => true,
+        ],
+    ]);
+
+    $discount->customerGroups()->sync([
+        $customerGroup->id => ['enabled' => true, 'starts_at' => now()],
+    ]);
+
+    $discount->channels()->sync([
+        $channel->id => ['enabled' => true, 'starts_at' => now()->subHour()],
+    ]);
+
+    $discount->discountableConditions()->create([
+        'discountable_type' => $productA->getMorphClass(),
+        'discountable_id' => $productA->id,
+    ]);
+
+    $discount->discountableRewards()->create([
+        'discountable_type' => $collection->getMorphClass(),
+        'discountable_id' => $collection->id,
+        'type' => 'reward',
+    ]);
+
+    $cart = $cart->calculate();
+
+    expect($cart->freeItems)->toBeNull();
+});
+
+test('automatically adds collection reward selecting in-stock product when others are out of stock', function () {
+    $customerGroup = CustomerGroup::factory()->create(['default' => true]);
+    $channel = Channel::factory()->create(['default' => true]);
+    $currency = Currency::factory()->create(['code' => 'GBP']);
+
+    $collection = Collection::factory()->create();
+
+    $productA = Product::factory()->create();
+    $productB = Product::factory()->create(); // out of stock
+    $productC = Product::factory()->create(); // in stock
+
+    $productB->collections()->sync($collection);
+    $productC->collections()->sync($collection);
+
+    $purchasableA = ProductVariant::factory()->create(['product_id' => $productA->id]);
+    $purchasableB = ProductVariant::factory()->create([
+        'product_id' => $productB->id,
+        'purchasable' => 'in_stock',
+        'stock' => 0,
+    ]);
+    $purchasableC = ProductVariant::factory()->create([
+        'product_id' => $productC->id,
+        'purchasable' => 'in_stock',
+        'stock' => 5,
+    ]);
+
+    $cart = Cart::factory()->create([
+        'channel_id' => $channel->id,
+        'currency_id' => $currency->id,
+    ]);
+
+    foreach ([$purchasableA, $purchasableB, $purchasableC] as $purchasable) {
+        Price::factory()->create([
+            'price' => 1000,
+            'min_quantity' => 1,
+            'currency_id' => $currency->id,
+            'priceable_type' => $purchasable->getMorphClass(),
+            'priceable_id' => $purchasable->id,
+        ]);
+    }
+
+    $cart->lines()->create([
+        'purchasable_type' => $purchasableA->getMorphClass(),
+        'purchasable_id' => $purchasableA->id,
+        'quantity' => 1,
+    ]);
+
+    $discount = Discount::factory()->create([
+        'type' => BuyXGetY::class,
+        'name' => 'Test Automatic Collection Reward Mixed Stock',
+        'data' => [
+            'min_qty' => 1,
+            'reward_qty' => 1,
+            'automatically_add_rewards' => true,
+        ],
+    ]);
+
+    $discount->customerGroups()->sync([
+        $customerGroup->id => ['enabled' => true, 'starts_at' => now()],
+    ]);
+
+    $discount->channels()->sync([
+        $channel->id => ['enabled' => true, 'starts_at' => now()->subHour()],
+    ]);
+
+    $discount->discountableConditions()->create([
+        'discountable_type' => $productA->getMorphClass(),
+        'discountable_id' => $productA->id,
+    ]);
+
+    $discount->discountableRewards()->create([
+        'discountable_type' => $collection->getMorphClass(),
+        'discountable_id' => $collection->id,
+        'type' => 'reward',
+    ]);
+
+    $cart = $cart->calculate();
+
+    // Only the in-stock product (C) should be added as a free item
+    expect($cart->freeItems)->toHaveCount(1);
+    expect($cart->freeItems->first()->id)->toEqual($productC->id);
+});
+
+test('automatically adds in-stock product reward when another reward product is out of stock', function () {
+    $customerGroup = CustomerGroup::factory()->create(['default' => true]);
+    $channel = Channel::factory()->create(['default' => true]);
+    $currency = Currency::factory()->create(['code' => 'GBP']);
+
+    $productA = Product::factory()->create(); // condition
+    $productB = Product::factory()->create(); // reward — out of stock
+    $productC = Product::factory()->create(); // reward — in stock
+
+    $purchasableA = ProductVariant::factory()->create(['product_id' => $productA->id]);
+    $purchasableB = ProductVariant::factory()->create([
+        'product_id' => $productB->id,
+        'purchasable' => 'in_stock',
+        'stock' => 0,
+    ]);
+    $purchasableC = ProductVariant::factory()->create([
+        'product_id' => $productC->id,
+        'purchasable' => 'in_stock',
+        'stock' => 5,
+    ]);
+
+    $cart = Cart::factory()->create([
+        'channel_id' => $channel->id,
+        'currency_id' => $currency->id,
+    ]);
+
+    foreach ([$purchasableA, $purchasableB, $purchasableC] as $purchasable) {
+        Price::factory()->create([
+            'price' => 1000,
+            'min_quantity' => 1,
+            'currency_id' => $currency->id,
+            'priceable_type' => $purchasable->getMorphClass(),
+            'priceable_id' => $purchasable->id,
+        ]);
+    }
+
+    $cart->lines()->create([
+        'purchasable_type' => $purchasableA->getMorphClass(),
+        'purchasable_id' => $purchasableA->id,
+        'quantity' => 1,
+    ]);
+
+    $discount = Discount::factory()->create([
+        'type' => BuyXGetY::class,
+        'name' => 'Test Automatic Reward Mixed Stock',
+        'data' => [
+            'min_qty' => 1,
+            'reward_qty' => 1,
+            'automatically_add_rewards' => true,
+        ],
+    ]);
+
+    $discount->customerGroups()->sync([
+        $customerGroup->id => ['enabled' => true, 'starts_at' => now()],
+    ]);
+
+    $discount->channels()->sync([
+        $channel->id => ['enabled' => true, 'starts_at' => now()->subHour()],
+    ]);
+
+    $discount->discountableConditions()->create([
+        'discountable_type' => $productA->getMorphClass(),
+        'discountable_id' => $productA->id,
+    ]);
+
+    // Both B (no stock) and C (in stock) are rewards
+    $discount->discountableRewards()->createMany([
+        ['discountable_type' => $productB->getMorphClass(), 'discountable_id' => $productB->id, 'type' => 'reward'],
+        ['discountable_type' => $productC->getMorphClass(), 'discountable_id' => $productC->id, 'type' => 'reward'],
+    ]);
+
+    $cart = $cart->calculate();
+
+    // Product C (in stock) must be added; product B (out of stock) must never be added
+    expect($cart->freeItems)->toHaveCount(1);
+    expect($cart->freeItems->first()->id)->toEqual($productC->id);
+});
+
 test('can add a multi quantity reward as a single line', function () {
     $customerGroup = CustomerGroup::factory()->create([
         'default' => true,
@@ -1826,6 +2131,82 @@
     expect($rewardLines->first()->quantity)->toEqual(3);
 });
 
+test('does not allocate a multi quantity reward beyond stock', function () {
+    $customerGroup = CustomerGroup::factory()->create(['default' => true]);
+    $channel = Channel::factory()->create(['default' => true]);
+    $currency = Currency::factory()->create(['code' => 'GBP']);
+
+    $productA = Product::factory()->create();
+    $productB = Product::factory()->create();
+
+    $purchasableA = ProductVariant::factory()->create(['product_id' => $productA->id]);
+    $purchasableB = ProductVariant::factory()->create([
+        'product_id' => $productB->id,
+        'purchasable' => 'in_stock',
+        'stock' => 1,
+    ]);
+
+    $cart = Cart::factory()->create([
+        'channel_id' => $channel->id,
+        'currency_id' => $currency->id,
+    ]);
+
+    foreach ([$purchasableA, $purchasableB] as $purchasable) {
+        Price::factory()->create([
+            'price' => 1000,
+            'min_quantity' => 1,
+            'currency_id' => $currency->id,
+            'priceable_type' => $purchasable->getMorphClass(),
+            'priceable_id' => $purchasable->id,
+        ]);
+    }
+
+    $cart->lines()->create([
+        'purchasable_type' => $purchasableA->getMorphClass(),
+        'purchasable_id' => $purchasableA->id,
+        'quantity' => 1,
+    ]);
+
+    $discount = Discount::factory()->create([
+        'type' => BuyXGetY::class,
+        'name' => 'Test Automatic Reward Limited Stock',
+        'data' => [
+            'min_qty' => 1,
+            'reward_qty' => 3,
+            'automatically_add_rewards' => true,
+        ],
+    ]);
+
+    $discount->customerGroups()->sync([
+        $customerGroup->id => ['enabled' => true, 'starts_at' => now()],
+    ]);
+
+    $discount->channels()->sync([
+        $channel->id => ['enabled' => true, 'starts_at' => now()->subHour()],
+    ]);
+
+    $discount->discountableConditions()->create([
+        'discountable_type' => $productA->getMorphClass(),
+        'discountable_id' => $productA->id,
+    ]);
+
+    $discount->discountableRewards()->create([
+        'discountable_type' => $productB->getMorphClass(),
+        'discountable_id' => $productB->id,
+        'type' => 'reward',
+    ]);
+
+    $cart->calculate();
+
+    $rewardLines = CartLine::where('cart_id', $cart->id)
+        ->where('purchasable_id', $purchasableB->id)
+        ->get();
+
+    // Only one unit is in stock, so only one is allocated despite reward_qty 3.
+    expect($rewardLines)->toHaveCount(1);
+    expect($rewardLines->first()->quantity)->toEqual(1);
+});
+
 test('can leave a reward line the shopper added at their own quantity', function () {
     $customerGroup = CustomerGroup::factory()->create([
         'default' => true,