diff --git a/src/Client.cc b/src/Client.cc
index eb197dbf..9ea84de9 100644
--- a/src/Client.cc
+++ b/src/Client.cc
@@ -438,9 +438,21 @@ bool Client::can_use_chat_commands() const {
 
 void Client::set_login(shared_ptr<Login> login) {
   this->login = login;
+
+  auto s = this->require_server_state();
+  if (!s->allow_same_account_concurrent_logins) {
+    auto it = s->client_for_account.find(login->account->account_id);
+    if ((it != s->client_for_account.end()) && (it->second.get() != this)) {
+      if (it->second->channel) {
+        it->second->channel->disconnect();
+      }
+      s->client_for_account.erase(it);
+    }
+    s->client_for_account.emplace(this->login->account->account_id, this->shared_from_this());
+  }
+
   if (this->log.should_log(phosg::LogLevel::L_INFO)) {
-    string login_str = this->login->str();
-    this->log.info_f("Login: {}", login_str);
+    this->log.info_f("Login: {}", this->login->str());
   }
 }
 
diff --git a/src/GameServer.cc b/src/GameServer.cc
index 75b8f528..a203e756 100644
--- a/src/GameServer.cc
+++ b/src/GameServer.cc
@@ -195,4 +195,11 @@ asio::awaitable<void> GameServer::destroy_client(std::shared_ptr<Client> c) {
       c->log.warning_f("Disconnect hook {} failed: {}", h_it.first, e.what());
     }
   }
+
+  if (c->login) {
+    auto it = this->state->client_for_account.find(c->login->account->account_id);
+    if ((it != this->state->client_for_account.end()) && (it->second == c)) {
+      this->state->client_for_account.erase(it);
+    }
+  }
 }
diff --git a/src/GameServer.hh b/src/GameServer.hh
index a0450fd0..a3956c7c 100644
--- a/src/GameServer.hh
+++ b/src/GameServer.hh
@@ -15,9 +15,7 @@ struct GameServerSocket : ServerSocket {
   ServerBehavior behavior;
 };
 
-class GameServer
-    : public Server<Client, GameServerSocket>,
-      public std::enable_shared_from_this<GameServer> {
+class GameServer : public Server<Client, GameServerSocket>, public std::enable_shared_from_this<GameServer> {
 public:
   GameServer() = delete;
   GameServer(const GameServer&) = delete;
diff --git a/src/ServerState.cc b/src/ServerState.cc
index cc1506ef..c4d6b5cf 100644
--- a/src/ServerState.cc
+++ b/src/ServerState.cc
@@ -865,6 +865,7 @@ void ServerState::load_config_early() {
   this->ip_stack_debug = this->config_json->get_bool("IPStackDebug", false);
   this->allow_unregistered_users = this->config_json->get_bool("AllowUnregisteredUsers", false);
   this->allow_pc_nte = this->config_json->get_bool("AllowPCNTE", false);
+  this->allow_same_account_concurrent_logins = this->config_json->get_bool("AllowSameAccountConcurrentLogins", false);
   this->allow_saving_accounts = this->config_json->get_bool("AllowSavingAccounts", true);
   this->use_temp_accounts_for_prototypes = this->config_json->get_bool("UseTemporaryAccountsForPrototypes", true);
   this->notify_server_for_max_level_achieved = this->config_json->get_bool("NotifyServerForMaxLevelAchieved", false);
diff --git a/src/ServerState.hh b/src/ServerState.hh
index f21aa228..e38e7484 100644
--- a/src/ServerState.hh
+++ b/src/ServerState.hh
@@ -127,6 +127,7 @@ struct ServerState : public std::enable_shared_from_this<ServerState> {
   bool allow_unregistered_users = false;
   bool allow_pc_nte = false;
   bool use_temp_accounts_for_prototypes = true;
+  bool allow_same_account_concurrent_logins = true;
   std::array<uint16_t, NUM_VERSIONS> compatibility_groups = {};
   bool enable_chat_commands = true;
   char chat_command_sentinel = '\0'; // 0 = default (@ on 11/2000; $ on all other versions)
@@ -312,6 +313,8 @@ struct ServerState : public std::enable_shared_from_this<ServerState> {
   uint8_t pre_lobby_event = 0;
   int32_t ep3_menu_song = -1;
 
+  std::unordered_map<uint32_t, std::shared_ptr<Client>> client_for_account;
+
   std::map<std::string, uint32_t> all_addresses;
   uint32_t local_address = 0;
   uint32_t external_address = 0;
diff --git a/system/config.example.json b/system/config.example.json
index 1d3c5716..17184310 100644
--- a/system/config.example.json
+++ b/system/config.example.json
@@ -226,6 +226,11 @@
   // Guild Card numbers every time they connect and cannot be banned by serial number or username.
   "AllowPCNTE": true,
 
+  // If this is enabled, players can log in multiple times on the same account at the same time. If this is disabled,
+  // only one login is allowed per account at a time; when a new session is opened, any existing sessions on the same
+  // account are disconnected.
+  "AllowSameAccountConcurrentLogins": true,
+
   // Whether to enable chat commands for all players. If this is true, all players will be able to use chat commands as
   // normal; if this is false, only players with the ALWAYS_ENABLE_CHAT_COMMANDS account flag will be able to use chat
   // commands.
diff --git a/tests/config.json b/tests/config.json
index 50ac3dc1..a133a9e6 100644
--- a/tests/config.json
+++ b/tests/config.json
@@ -190,6 +190,7 @@
   "AllowUnregisteredUsers": true,
   "UseTemporaryAccountsForPrototypes": true,
   "AllowPCNTE": true,
+  "AllowSameAccountConcurrentLogins": true,
   "EnableChatCommands": true,
   "CompatibilityGroups": [0x0000, 0x0000, 0x0004, 0x0008, 0x00B0, 0x00B0, 0x0040, 0x00B0, 0x0100, 0x1200, 0x0400, 0x0800, 0x1200, 0x2000],
   "VersionNameColors": [