diff --git a/src/client/HostLobbyModal.ts b/src/client/HostLobbyModal.ts
index d9cf6930a..079beca70 100644
--- a/src/client/HostLobbyModal.ts
+++ b/src/client/HostLobbyModal.ts
@@ -633,6 +633,11 @@ export class HostLobbyModal extends BaseModal {
   }
 
   protected onOpen(): void {
+    // Re-armed here (not in onClose's reset) so that once
+    // closeWithoutLeaving() disarms it, no close cascade — e.g. another
+    // modal's close() navigating via showPage, which force-closes this one —
+    // can re-arm it and disconnect the host mid game-start.
+    this.leaveLobbyOnClose = true;
     this.startLobbyUpdates();
     void getUserMe().then((userMe) => {
       // Dev skips the subscription gate (matching the server) so the
@@ -695,6 +700,21 @@ export class HostLobbyModal extends BaseModal {
     );
   }
 
+  // Close as part of the lobby -> game transition (e.g. auto-start of a
+  // listed lobby): the host is entering the game, not leaving the lobby, so
+  // closing must not disconnect them (the server would tear the lobby down).
+  // disarmLeaveOnClose is separate because closing ANY page-modal navigates
+  // via showPage, which force-closes the currently visible page — so all
+  // lobby modals must be disarmed before any of them is closed.
+  public disarmLeaveOnClose() {
+    this.leaveLobbyOnClose = false;
+  }
+
+  public closeWithoutLeaving() {
+    this.disarmLeaveOnClose();
+    this.close();
+  }
+
   public confirmBeforeClose(): boolean | Promise<boolean> {
     return this.confirmClose(translateText("host_modal.leave_confirmation"));
   }
@@ -765,8 +785,6 @@ export class HostLobbyModal extends BaseModal {
     this.publiclyListed = false;
     this.showSubscriptionRequired = false;
     this.autoStartAt = null;
-
-    this.leaveLobbyOnClose = true;
   }
 
   private async handleSelectRandomMap() {
diff --git a/src/client/JoinLobbyModal.ts b/src/client/JoinLobbyModal.ts
index e098472a8..cdc603763 100644
--- a/src/client/JoinLobbyModal.ts
+++ b/src/client/JoinLobbyModal.ts
@@ -338,6 +338,10 @@ export class JoinLobbyModal extends BaseModal {
   }
 
   protected onOpen(args?: Record<string, unknown>): void {
+    // Re-armed here (not in onClose's reset) so that once
+    // disarmLeaveOnClose() runs, no close cascade can re-arm it and
+    // disconnect the player mid game-start.
+    this.leaveLobbyOnClose = true;
     void this.hostedLobbySocket.start();
     const lobbyId = typeof args?.lobbyId === "string" ? args.lobbyId : "";
     const lobbyInfo = args?.lobbyInfo as GameInfo | PublicGameInfo | undefined;
@@ -453,7 +457,6 @@ export class JoinLobbyModal extends BaseModal {
     this.serverTimeOffset = 0;
     this.lobbyCreatorClientID = null;
     this.isConnecting = true;
-    this.leaveLobbyOnClose = true;
   }
 
   disconnectedCallback() {
@@ -474,8 +477,17 @@ export class JoinLobbyModal extends BaseModal {
     this.close();
   }
 
-  public closeWithoutLeaving() {
+  // Closing this modal is part of the game-start transition, not the player
+  // leaving. Kept separate from closeWithoutLeaving because closing ANY
+  // page-modal navigates via showPage, which force-closes the currently
+  // visible page — so all lobby modals must be disarmed before any of them
+  // is closed.
+  public disarmLeaveOnClose() {
     this.leaveLobbyOnClose = false;
+  }
+
+  public closeWithoutLeaving() {
+    this.disarmLeaveOnClose();
     this.close();
   }
 
diff --git a/src/client/Main.ts b/src/client/Main.ts
index 3ec47f8a9..c0ed52717 100644
--- a/src/client/Main.ts
+++ b/src/client/Main.ts
@@ -869,10 +869,17 @@ class Client {
       document
         .getElementById("username-validation-error")
         ?.classList.add("hidden");
+      // Disarm BOTH lobby modals before closing either: closing any
+      // page-modal navigates via showPage, which force-closes the currently
+      // visible page — the other lobby modal. If that one is still armed,
+      // its onClose leaves the lobby and disconnects the player mid
+      // game-start (host or joiner, depending on close order).
+      this.hostModal?.disarmLeaveOnClose();
+      this.joinModal?.disarmLeaveOnClose();
+      this.hostModal?.closeWithoutLeaving();
       this.joinModal?.closeWithoutLeaving();
       [
         "single-player-modal",
-        "host-lobby-modal",
         "game-starting-modal",
         "game-top-bar",
         "help-modal",
diff --git a/src/server/GameServer.ts b/src/server/GameServer.ts
index 0afb2f5f3..b321f380a 100644
--- a/src/server/GameServer.ts
+++ b/src/server/GameServer.ts
@@ -762,7 +762,10 @@ export class GameServer {
       (c) => c.clientID !== client.clientID,
     );
 
-    if (this._hasStarted) {
+    // hasStarted() includes prestart: during the lobby -> game transition
+    // clients reconnect, and a host socket closing then must not tear the
+    // starting game down.
+    if (this.hasStarted()) {
       return;
     }
     // Remove persistentId if the game has not started to prevent going over max players
diff --git a/tests/server/HostedLobbyListing.test.ts b/tests/server/HostedLobbyListing.test.ts
index b052308c8..1f8ce75ae 100644
--- a/tests/server/HostedLobbyListing.test.ts
+++ b/tests/server/HostedLobbyListing.test.ts
@@ -332,6 +332,23 @@ describe("host-left lobby teardown", () => {
     (game as any)._hasEnded = true;
     expect(game.joinClient({} as any)).toBe("rejected");
   });
+
+  it("does not tear down when the host disconnects during prestart", () => {
+    // During the lobby -> game transition the host modal closes and sockets
+    // churn; a starting game (e.g. listed-lobby auto-start) must survive it.
+    const gm = new GameManager(mockLogger);
+    const game = gm.createGame("g-prestart", undefined, CREATOR)!;
+    game.setListed(true);
+
+    const hostWs = fakeWs();
+    game.joinClient(makeClient("host", CREATOR, hostWs));
+    (game as any)._hasPrestarted = true;
+
+    hostWs.emit("close");
+
+    expect((game as any)._hasEnded).toBe(false);
+    expect(game.phase()).not.toBe(GamePhase.Finished);
+  });
 });
 
 describe("listed lobby host powers", () => {