diff --git a/src/CommandFormats.hh b/src/CommandFormats.hh
index 2aa8b908..93a4ed9a 100644
--- a/src/CommandFormats.hh
+++ b/src/CommandFormats.hh
@@ -5959,6 +5959,11 @@ struct G_SyncCardTradeServerState_Ep3_6xBB {
 
 // 6xBB: BB bank request (handled by the server)
 
+struct G_RequestBankContents_BB_6xBB {
+  G_UnusedHeader header;
+  le_uint32_t checksum; // crc32 of the bank contents in memory
+} __packed_ws__(G_RequestBankContents_BB_6xBB, 0x08);
+
 // 6xBC: Card counts (Episode 3)
 // This is sent by the client in response to a 6xB5x38 command. This is used
 // along with 6xB5x38 so clients can see each other's card counts. Curiously,
@@ -5980,6 +5985,9 @@ struct G_CardCounts_Ep3_6xBC {
 } __packed_ws__(G_CardCounts_Ep3_6xBC, 0x2FC);
 
 // 6xBC: BB bank contents (server->client only)
+// This is sent in response to a 6xBB command. If the checksum in this command
+// doesn't match the checksum the client sent in its 6xBB command, the client
+// overwrites its bank data with the data sent in this command.
 
 struct G_BankContentsHeader_BB_6xBC {
   G_ExtendedHeaderT<G_UnusedHeader> header;
diff --git a/src/PlayerInventory.hh b/src/PlayerInventory.hh
index 87d2fe67..774b6196 100644
--- a/src/PlayerInventory.hh
+++ b/src/PlayerInventory.hh
@@ -305,6 +305,10 @@ struct PlayerBankT {
   /* 0008 */ parray<PlayerBankItemT<BE>, SlotCount> items;
   /* 05A8 for 60 items (v1/v2), 12C8 for 200 items (v3/v4) */
 
+  uint32_t checksum() const {
+    return phosg::crc32(this, 2 * sizeof(U32T<BE>) + sizeof(PlayerBankItemT<BE>) * min<size_t>(SlotCount, this->num_items));
+  }
+
   void add_item(const ItemData& item, const ItemData::StackLimits& limits) {
     uint32_t primary_identifier = item.primary_identifier();
 
diff --git a/src/SendCommands.cc b/src/SendCommands.cc
index 0c22bada..ea54c8fb 100644
--- a/src/SendCommands.cc
+++ b/src/SendCommands.cc
@@ -3045,9 +3045,7 @@ void send_bank(shared_ptr<Client> c) {
 
   G_BankContentsHeader_BB_6xBC cmd = {
       {{0xBC, 0, 0}, sizeof(G_BankContentsHeader_BB_6xBC) + items.size() * sizeof(PlayerBankItem)},
-      phosg::random_object<uint32_t>(),
-      bank.num_items,
-      bank.meseta};
+      bank.checksum(), bank.num_items, bank.meseta};
 
   send_command_t_vt(c, 0x6C, 0x00, cmd, items);
 }