diff --git a/include/game/game_handler.hpp b/include/game/game_handler.hpp
index b6c86794..a121d440 100644
--- a/include/game/game_handler.hpp
+++ b/include/game/game_handler.hpp
@@ -1990,7 +1990,7 @@ public:
     void auctionSearch(const std::string& name, uint8_t levelMin, uint8_t levelMax,
                        uint32_t quality, uint32_t itemClass, uint32_t itemSubClass,
                        uint32_t invTypeMask, uint8_t usableOnly, uint32_t offset = 0);
-    void auctionSellItem(uint64_t itemGuid, uint32_t stackCount, uint32_t bid,
+    void auctionSellItem(int backpackIndex, uint32_t bid,
                          uint32_t buyout, uint32_t duration);
     void auctionPlaceBid(uint32_t auctionId, uint32_t amount);
     void auctionBuyout(uint32_t auctionId, uint32_t buyoutPrice);
diff --git a/include/game/inventory_handler.hpp b/include/game/inventory_handler.hpp
index 3c4574c9..15c5b5b7 100644
--- a/include/game/inventory_handler.hpp
+++ b/include/game/inventory_handler.hpp
@@ -194,7 +194,7 @@ public:
     void auctionSearch(const std::string& name, uint8_t levelMin, uint8_t levelMax,
                        uint32_t quality, uint32_t itemClass, uint32_t itemSubClass,
                        uint32_t invTypeMask, uint8_t usableOnly, uint32_t offset = 0);
-    void auctionSellItem(uint64_t itemGuid, uint32_t stackCount, uint32_t bid,
+    void auctionSellItem(int backpackIndex, uint32_t bid,
                          uint32_t buyout, uint32_t duration);
     void auctionPlaceBid(uint32_t auctionId, uint32_t amount);
     void auctionBuyout(uint32_t auctionId, uint32_t buyoutPrice);
diff --git a/include/game/world_packets.hpp b/include/game/world_packets.hpp
index d0f98577..19cbf3ba 100644
--- a/include/game/world_packets.hpp
+++ b/include/game/world_packets.hpp
@@ -2736,7 +2736,8 @@ class AuctionSellItemPacket {
 public:
     static network::Packet build(uint64_t auctioneerGuid, uint64_t itemGuid,
                                   uint32_t stackCount, uint32_t bid,
-                                  uint32_t buyout, uint32_t duration);
+                                  uint32_t buyout, uint32_t duration,
+                                  bool preWotlk = false);
 };
 
 /** CMSG_AUCTION_PLACE_BID packet builder */
diff --git a/src/game/game_handler.cpp b/src/game/game_handler.cpp
index c4bd725a..f955cca9 100644
--- a/src/game/game_handler.cpp
+++ b/src/game/game_handler.cpp
@@ -6640,9 +6640,9 @@ void GameHandler::auctionSearch(const std::string& name, uint8_t levelMin, uint8
     if (inventoryHandler_) inventoryHandler_->auctionSearch(name, levelMin, levelMax, quality, itemClass, itemSubClass, invTypeMask, usableOnly, offset);
 }
 
-void GameHandler::auctionSellItem(uint64_t itemGuid, uint32_t stackCount,
-                                    uint32_t bid, uint32_t buyout, uint32_t duration) {
-    if (inventoryHandler_) inventoryHandler_->auctionSellItem(itemGuid, stackCount, bid, buyout, duration);
+void GameHandler::auctionSellItem(int backpackIndex, uint32_t bid,
+                                    uint32_t buyout, uint32_t duration) {
+    if (inventoryHandler_) inventoryHandler_->auctionSellItem(backpackIndex, bid, buyout, duration);
 }
 
 void GameHandler::auctionPlaceBid(uint32_t auctionId, uint32_t amount) {
diff --git a/src/game/inventory_handler.cpp b/src/game/inventory_handler.cpp
index 74903f86..d81f444d 100644
--- a/src/game/inventory_handler.cpp
+++ b/src/game/inventory_handler.cpp
@@ -1860,10 +1860,25 @@ void InventoryHandler::auctionSearch(const std::string& name, uint8_t levelMin,
     auctionSearchDelayTimer_ = 5.0f;
 }
 
-void InventoryHandler::auctionSellItem(uint64_t itemGuid, uint32_t stackCount, uint32_t bid,
+void InventoryHandler::auctionSellItem(int backpackIndex, uint32_t bid,
                                         uint32_t buyout, uint32_t duration) {
     if (owner_.state != WorldState::IN_WORLD || !owner_.socket || auctioneerGuid_ == 0) return;
-    auto packet = AuctionSellItemPacket::build(auctioneerGuid_, itemGuid, stackCount, bid, buyout, duration);
+    if (backpackIndex < 0 || backpackIndex >= owner_.inventory.getBackpackSize()) return;
+    const auto& slot = owner_.inventory.getBackpackSlot(backpackIndex);
+    if (slot.empty()) return;
+
+    uint64_t itemGuid = owner_.backpackSlotGuids_[backpackIndex];
+    if (itemGuid == 0) {
+        itemGuid = owner_.resolveOnlineItemGuid(slot.item.itemId);
+    }
+    if (itemGuid == 0) {
+        LOG_ERROR("auctionSellItem: could not resolve GUID for backpack slot ", backpackIndex);
+        return;
+    }
+
+    uint32_t stackCount = slot.item.stackCount;
+    auto packet = AuctionSellItemPacket::build(auctioneerGuid_, itemGuid, stackCount, bid, buyout, duration,
+                                                isPreWotlk());
     owner_.socket->send(packet);
 }
 
diff --git a/src/game/world_packets.cpp b/src/game/world_packets.cpp
index e5753b70..4867b295 100644
--- a/src/game/world_packets.cpp
+++ b/src/game/world_packets.cpp
@@ -5726,13 +5726,20 @@ network::Packet AuctionListItemsPacket::build(
 network::Packet AuctionSellItemPacket::build(
     uint64_t auctioneerGuid, uint64_t itemGuid,
     uint32_t stackCount, uint32_t bid,
-    uint32_t buyout, uint32_t duration)
+    uint32_t buyout, uint32_t duration,
+    bool preWotlk)
 {
     network::Packet p(wireOpcode(Opcode::CMSG_AUCTION_SELL_ITEM));
     p.writeUInt64(auctioneerGuid);
-    p.writeUInt32(1);  // item count (WotLK supports multiple, we send 1)
-    p.writeUInt64(itemGuid);
-    p.writeUInt32(stackCount);
+    if (!preWotlk) {
+        // WotLK: itemCount(4) + per-item [guid(8) + stackCount(4)]
+        p.writeUInt32(1);
+        p.writeUInt64(itemGuid);
+        p.writeUInt32(stackCount);
+    } else {
+        // Classic/TBC: just itemGuid, no count fields
+        p.writeUInt64(itemGuid);
+    }
     p.writeUInt32(bid);
     p.writeUInt32(buyout);
     p.writeUInt32(duration);
diff --git a/src/ui/window_manager.cpp b/src/ui/window_manager.cpp
index b7a516dc..19e1c81f 100644
--- a/src/ui/window_manager.cpp
+++ b/src/ui/window_manager.cpp
@@ -3375,16 +3375,11 @@ void WindowManager::renderAuctionHouseWindow(game::GameHandler& gameHandler,
                                   + static_cast<uint32_t>(auctionSellBuyout_[2]);
             const uint32_t durationMins[] = {720, 1440, 2880};
             uint32_t dur = durationMins[auctionSellDuration_];
-            uint64_t itemGuid = gameHandler.getBackpackItemGuid(auctionSellSlotIndex_);
-            const auto& slot = gameHandler.getInventory().getBackpackSlot(auctionSellSlotIndex_);
-            uint32_t stackCount = slot.item.stackCount;
-            if (itemGuid != 0) {
-                gameHandler.auctionSellItem(itemGuid, stackCount, bidCopper, buyoutCopper, dur);
-                // Clear sell inputs
-                auctionSellSlotIndex_ = -1;
-                auctionSellBid_[0] = auctionSellBid_[1] = auctionSellBid_[2] = 0;
-                auctionSellBuyout_[0] = auctionSellBuyout_[1] = auctionSellBuyout_[2] = 0;
-            }
+            gameHandler.auctionSellItem(auctionSellSlotIndex_, bidCopper, buyoutCopper, dur);
+            // Clear sell inputs
+            auctionSellSlotIndex_ = -1;
+            auctionSellBid_[0] = auctionSellBid_[1] = auctionSellBid_[2] = 0;
+            auctionSellBuyout_[0] = auctionSellBuyout_[1] = auctionSellBuyout_[2] = 0;
         }
         if (!canCreate) ImGui::EndDisabled();