diff --git a/src/PlayerSubordinates.cc b/src/PlayerSubordinates.cc
index 3e1bd957..fca44136 100644
--- a/src/PlayerSubordinates.cc
+++ b/src/PlayerSubordinates.cc
@@ -265,7 +265,7 @@ void PlayerLobbyDataXB::clear() {
 void PlayerLobbyDataBB::clear() {
   this->player_tag = 0;
   this->guild_card_number = 0;
-  this->sys_guild_card_number = 0;
+  this->team_master_guild_card_number = 0;
   this->team_id = 0;
   this->unknown_a1.clear(0);
   this->client_id = 0;
diff --git a/src/PlayerSubordinates.hh b/src/PlayerSubordinates.hh
index 7f6cfc98..28066e5c 100644
--- a/src/PlayerSubordinates.hh
+++ b/src/PlayerSubordinates.hh
@@ -310,7 +310,7 @@ struct PlayerLobbyDataXB {
 struct PlayerLobbyDataBB {
   /* 00 */ le_uint32_t player_tag = 0;
   /* 04 */ le_uint32_t guild_card_number = 0;
-  /* 08 */ le_uint32_t sys_guild_card_number = 0;
+  /* 08 */ le_uint32_t team_master_guild_card_number = 0;
   /* 0C */ le_uint32_t team_id = 0;
   /* 10 */ parray<uint8_t, 0x0C> unknown_a1;
   /* 1C */ le_uint32_t client_id = 0;
diff --git a/src/SaveFileFormats.hh b/src/SaveFileFormats.hh
index e959c648..5da10b92 100644
--- a/src/SaveFileFormats.hh
+++ b/src/SaveFileFormats.hh
@@ -134,7 +134,7 @@ struct PSOBBMinimalSystemFile {
 } __attribute__((packed));
 
 struct PSOBBTeamMembership {
-  /* 0000 */ le_uint32_t guild_card_number = 0;
+  /* 0000 */ le_uint32_t team_master_guild_card_number = 0;
   /* 0004 */ le_uint32_t team_id = 0;
   /* 0008 */ le_uint32_t unknown_a5 = 0;
   /* 000C */ le_uint32_t unknown_a6 = 0;
diff --git a/src/SendCommands.cc b/src/SendCommands.cc
index eafcb07d..528ad979 100644
--- a/src/SendCommands.cc
+++ b/src/SendCommands.cc
@@ -1644,11 +1644,14 @@ template <>
 void populate_lobby_data_for_client<PlayerLobbyDataBB>(PlayerLobbyDataBB& ret, shared_ptr<const Client> c, shared_ptr<const Client> viewer_c) {
   ret.player_tag = 0x00010000;
   ret.guild_card_number = c->license->serial_number;
-  ret.sys_guild_card_number = viewer_c->license->serial_number;
   ret.client_id = c->lobby_client_id;
   auto team = c->team();
   if (team) {
+    ret.team_master_guild_card_number = team->master_serial_number;
     ret.team_id = team->team_id;
+  } else {
+    ret.team_master_guild_card_number = 0;
+    ret.team_id = 0;
   }
   string name = c->character()->disp.name.decode(c->language());
   if ((name.size() >= 2) && (name[0] == '\t') && (name[1] != 'C')) {
diff --git a/src/TeamIndex.cc b/src/TeamIndex.cc
index b2de7dd9..5d606978 100644
--- a/src/TeamIndex.cc
+++ b/src/TeamIndex.cc
@@ -58,6 +58,9 @@ void TeamIndex::Team::load_config() {
     Member m(*member_it);
     this->points += m.points;
     uint32_t serial_number = m.serial_number;
+    if (m.check_flag(Member::Flag::IS_MASTER)) {
+      this->master_serial_number = serial_number;
+    }
     this->members.emplace(serial_number, std::move(m));
   }
   try {
@@ -125,7 +128,7 @@ PSOBBTeamMembership TeamIndex::Team::membership_for_member(uint32_t serial_numbe
   const auto& m = this->members.at(serial_number);
 
   PSOBBTeamMembership ret;
-  ret.guild_card_number = serial_number;
+  ret.team_master_guild_card_number = this->master_serial_number;
   ret.team_id = this->team_id;
   ret.unknown_a5 = 0;
   ret.unknown_a6 = 0;
@@ -421,6 +424,7 @@ void TeamIndex::change_master(uint32_t master_serial_number, uint32_t new_master
   master_m.set_flag(TeamIndex::Team::Member::Flag::IS_LEADER);
   new_master_m.clear_flag(TeamIndex::Team::Member::Flag::IS_LEADER);
   new_master_m.set_flag(TeamIndex::Team::Member::Flag::IS_MASTER);
+  team->master_serial_number = new_master_serial_number;
   team->save_config();
 }
 
diff --git a/src/TeamIndex.hh b/src/TeamIndex.hh
index 852717be..ac7303f8 100644
--- a/src/TeamIndex.hh
+++ b/src/TeamIndex.hh
@@ -60,6 +60,7 @@ public:
     uint32_t points = 0;
     uint32_t spent_points = 0;
     std::string name;
+    uint32_t master_serial_number = 0;
     std::unordered_map<uint32_t, Member> members;
     uint32_t reward_flags = 0;
     std::unordered_set<std::string> reward_keys;