diff --git a/src/client/ClientGameRunner.ts b/src/client/ClientGameRunner.ts
index df11c56c8..d3a63e0cb 100644
--- a/src/client/ClientGameRunner.ts
+++ b/src/client/ClientGameRunner.ts
@@ -13,7 +13,7 @@ import {
 import { createGameRecord } from "../core/Util";
 import { ServerConfig } from "../core/configuration/Config";
 import { getConfig } from "../core/configuration/ConfigLoader";
-import { Cell, UnitType } from "../core/game/Game";
+import { UnitType } from "../core/game/Game";
 import { TileRef } from "../core/game/GameMap";
 import {
   ErrorUpdate,
@@ -390,22 +390,15 @@ export class ClientGameRunner {
         this.gameView.isLand(tile)
       ) {
         this.myPlayer
-          .bestTransportShipSpawn(this.gameView.ref(cell.x, cell.y))
+          .bestTransportShipSpawn(tile)
           .then((spawn: number | false) => {
             if (this.myPlayer === null) throw new Error("not initialized");
-            let spawnCell: Cell | null = null;
-            if (spawn !== false) {
-              spawnCell = new Cell(
-                this.gameView.x(spawn),
-                this.gameView.y(spawn),
-              );
-            }
             this.eventBus.emit(
               new SendBoatAttackIntentEvent(
                 this.gameView.owner(tile).id(),
-                cell,
+                tile,
                 this.myPlayer.troops() * this.renderer.uiState.attackRatio,
-                spawnCell,
+                spawn !== false ? spawn : null,
               ),
             );
           });
diff --git a/src/client/Transport.ts b/src/client/Transport.ts
index 0cc38ff70..3ee134ffc 100644
--- a/src/client/Transport.ts
+++ b/src/client/Transport.ts
@@ -10,6 +10,7 @@ import {
   Tick,
   UnitType,
 } from "../core/game/Game";
+import { TileRef } from "../core/game/GameMap";
 import { PlayerView } from "../core/game/GameView";
 import {
   AllPlayersStats,
@@ -69,9 +70,9 @@ export class SendAttackIntentEvent implements GameEvent {
 export class SendBoatAttackIntentEvent implements GameEvent {
   constructor(
     public readonly targetID: PlayerID | null,
-    public readonly dst: Cell,
+    public readonly dst: TileRef,
     public readonly troops: number,
-    public readonly src: Cell | null = null,
+    public readonly src: TileRef | null = null,
   ) {}
 }
 
@@ -432,10 +433,8 @@ export class Transport {
       clientID: this.lobbyConfig.clientID,
       targetID: event.targetID,
       troops: event.troops,
-      dstX: event.dst.x,
-      dstY: event.dst.y,
-      srcX: event.src?.x ?? null,
-      srcY: event.src?.y ?? null,
+      dst: event.dst,
+      src: event.src,
     });
   }
 
diff --git a/src/client/graphics/layers/RadialMenu.ts b/src/client/graphics/layers/RadialMenu.ts
index db79c507e..d07dfe699 100644
--- a/src/client/graphics/layers/RadialMenu.ts
+++ b/src/client/graphics/layers/RadialMenu.ts
@@ -287,6 +287,9 @@ export class RadialMenu implements Layer {
     if (!this.isVisible || this.clickedCell === null) return;
     const myPlayer = this.g.myPlayer();
     if (myPlayer === null || !myPlayer.isAlive()) return;
+    if (!this.g.isValidCoord(this.clickedCell.x, this.clickedCell.y)) {
+      return;
+    }
     const tile = this.g.ref(this.clickedCell.x, this.clickedCell.y);
     if (this.originalTileOwner.isPlayer()) {
       if (this.g.owner(tile) !== this.originalTileOwner) {
@@ -399,18 +402,12 @@ export class RadialMenu implements Layer {
         // BestTransportShipSpawn is an expensive operation, so
         // we calculate it here and send the spawn tile to other clients.
         myPlayer.bestTransportShipSpawn(tile).then((spawn) => {
-          let spawnTile: Cell | null = null;
-          if (spawn !== false) {
-            spawnTile = new Cell(this.g.x(spawn), this.g.y(spawn));
-          }
-
-          if (this.clickedCell === null) return;
           this.eventBus.emit(
             new SendBoatAttackIntentEvent(
               this.g.owner(tile).id(),
-              this.clickedCell,
+              tile,
               this.uiState.attackRatio * myPlayer.troops(),
-              spawnTile,
+              spawn !== false ? spawn : null,
             ),
           );
         });
diff --git a/src/core/Schemas.ts b/src/core/Schemas.ts
index 375aa8956..902b75c76 100644
--- a/src/core/Schemas.ts
+++ b/src/core/Schemas.ts
@@ -198,10 +198,8 @@ export const BoatAttackIntentSchema = BaseIntentSchema.extend({
   type: z.literal("boat"),
   targetID: ID.nullable(),
   troops: z.number(),
-  dstX: z.number(),
-  dstY: z.number(),
-  srcX: z.number().nullable(),
-  srcY: z.number().nullable(),
+  dst: z.number(),
+  src: z.number().nullable(),
 });
 
 export const AllianceRequestIntentSchema = BaseIntentSchema.extend({
diff --git a/src/core/execution/ExecutionManager.ts b/src/core/execution/ExecutionManager.ts
index aec3516f2..192c0f9a8 100644
--- a/src/core/execution/ExecutionManager.ts
+++ b/src/core/execution/ExecutionManager.ts
@@ -1,5 +1,4 @@
 import { Execution, Game } from "../game/Game";
-import { TileRef } from "../game/GameMap";
 import { PseudoRandom } from "../PseudoRandom";
 import { ClientID, GameID, Intent, Turn } from "../Schemas";
 import { simpleHash } from "../Util";
@@ -70,16 +69,12 @@ export class Executor {
           this.mg.ref(intent.x, intent.y),
         );
       case "boat":
-        let src: TileRef | null = null;
-        if (intent.srcX !== null && intent.srcY !== null) {
-          src = this.mg.ref(intent.srcX, intent.srcY);
-        }
         return new TransportShipExecution(
           playerID,
           intent.targetID,
-          this.mg.ref(intent.dstX, intent.dstY),
+          intent.dst,
           intent.troops,
-          src,
+          intent.src,
         );
       case "allianceRequest":
         return new AllianceRequestExecution(playerID, intent.recipient);
diff --git a/src/core/execution/MoveWarshipExecution.ts b/src/core/execution/MoveWarshipExecution.ts
index 13431bc1d..0a0aad166 100644
--- a/src/core/execution/MoveWarshipExecution.ts
+++ b/src/core/execution/MoveWarshipExecution.ts
@@ -9,6 +9,10 @@ export class MoveWarshipExecution implements Execution {
   ) {}
 
   init(mg: Game, ticks: number): void {
+    if (!mg.isValidRef(this.position)) {
+      console.warn(`MoveWarshipExecution: position ${this.position} not valid`);
+      return;
+    }
     const warship = this.owner
       .units(UnitType.Warship)
       .find((u) => u.id() === this.unitId);
diff --git a/src/core/execution/TransportShipExecution.ts b/src/core/execution/TransportShipExecution.ts
index 8851d8fdf..d40326435 100644
--- a/src/core/execution/TransportShipExecution.ts
+++ b/src/core/execution/TransportShipExecution.ts
@@ -60,6 +60,16 @@ export class TransportShipExecution implements Execution {
       this.active = false;
       return;
     }
+    if (!mg.isValidRef(this.ref)) {
+      console.warn(`TransportShipExecution: ref ${this.ref} not valid`);
+      this.active = false;
+      return;
+    }
+    if (this.src !== null && !mg.isValidRef(this.src)) {
+      console.warn(`TransportShipExecution: src ${this.src} not valid`);
+      this.active = false;
+      return;
+    }
 
     this.lastMove = ticks;
     this.mg = mg;
diff --git a/src/core/game/GameImpl.ts b/src/core/game/GameImpl.ts
index 3a5fb80ef..c8b1ee586 100644
--- a/src/core/game/GameImpl.ts
+++ b/src/core/game/GameImpl.ts
@@ -687,6 +687,9 @@ export class GameImpl implements Game {
   ref(x: number, y: number): TileRef {
     return this._map.ref(x, y);
   }
+  isValidRef(ref: TileRef): boolean {
+    return this._map.isValidRef(ref);
+  }
   x(ref: TileRef): number {
     return this._map.x(ref);
   }
diff --git a/src/core/game/GameMap.ts b/src/core/game/GameMap.ts
index 3a9356f3b..6081cafa3 100644
--- a/src/core/game/GameMap.ts
+++ b/src/core/game/GameMap.ts
@@ -5,7 +5,7 @@ export type TileUpdate = bigint;
 
 export interface GameMap {
   ref(x: number, y: number): TileRef;
-
+  isValidRef(ref: TileRef): boolean;
   x(ref: TileRef): number;
   y(ref: TileRef): number;
   cell(ref: TileRef): Cell;
@@ -117,6 +117,10 @@ export class GameMapImpl implements GameMap {
     return this.yToRef[y] + x;
   }
 
+  isValidRef(ref: TileRef): boolean {
+    return this.isValidCoord(this.x(ref), this.y(ref));
+  }
+
   x(ref: TileRef): number {
     return this.refToX[ref];
   }
diff --git a/src/core/game/GameView.ts b/src/core/game/GameView.ts
index e820c2234..839155647 100644
--- a/src/core/game/GameView.ts
+++ b/src/core/game/GameView.ts
@@ -481,6 +481,9 @@ export class GameView implements GameMap {
   ref(x: number, y: number): TileRef {
     return this._map.ref(x, y);
   }
+  isValidRef(ref: TileRef): boolean {
+    return this._map.isValidRef(ref);
+  }
   x(ref: TileRef): number {
     return this._map.x(ref);
   }