diff --git a/src/game/game_handler.cpp b/src/game/game_handler.cpp
index a870ddcc..0ead0468 100644
--- a/src/game/game_handler.cpp
+++ b/src/game/game_handler.cpp
@@ -15821,8 +15821,11 @@ void GameHandler::buyItem(uint64_t vendorGuid, uint32_t itemId, uint32_t slot, u
     packet.writeUInt32(itemId); // item entry
     packet.writeUInt32(slot);   // vendor slot index
     packet.writeUInt32(count);
-    // WotLK/AzerothCore expects a trailing byte here.
-    packet.writeUInt8(0);
+    // WotLK/AzerothCore expects a trailing byte; Classic/TBC do not
+    const bool isWotLk = isActiveExpansion("wotlk");
+    if (isWotLk) {
+        packet.writeUInt8(0);
+    }
     socket->send(packet);
 }
 
diff --git a/src/game/world_packets.cpp b/src/game/world_packets.cpp
index b7d8075b..5d3989c7 100644
--- a/src/game/world_packets.cpp
+++ b/src/game/world_packets.cpp
@@ -3828,7 +3828,9 @@ network::Packet BuyItemPacket::build(uint64_t vendorGuid, uint32_t itemId, uint3
     packet.writeUInt32(itemId);  // item entry
     packet.writeUInt32(slot);    // vendor slot index from SMSG_LIST_INVENTORY
     packet.writeUInt32(count);
-    // WotLK/AzerothCore expects a trailing byte on CMSG_BUY_ITEM.
+    // Note: WotLK/AzerothCore expects a trailing byte; Classic/TBC do not.
+    // This static helper always adds it (appropriate for CMaNGOS/AzerothCore).
+    // For Classic/TBC, use the GameHandler::buyItem() path which checks expansion.
     packet.writeUInt8(0);
     return packet;
 }