diff --git a/src/core/execution/PlayerExecution.ts b/src/core/execution/PlayerExecution.ts
index 987114028..a6775d812 100644
--- a/src/core/execution/PlayerExecution.ts
+++ b/src/core/execution/PlayerExecution.ts
@@ -123,8 +123,9 @@ export class PlayerExecution implements Execution {
     const enemies = new Set<number>();
     for (const ref of cluster) {
       if (
-        this.mg.isOceanShore(ref) ||
-        this.mg.neighbors(ref).some((n) => !this.mg.hasOwner(n))
+        this.mg.isOceanShore(tile) ||
+        this.mg.isOnEdgeOfMap(tile) ||
+        this.mg.neighbors(tile).some((n) => !this.mg.hasOwner(n))
       ) {
         return false;
       }
@@ -145,7 +146,7 @@ export class PlayerExecution implements Execution {
   private isSurrounded(cluster: Set<TileRef>): boolean {
     let enemyTiles = new Set<TileRef>();
     for (const tr of cluster) {
-      if (this.mg.isOceanShore(tr)) {
+      if (this.mg.isOceanShore(tr) || this.mg.isOnEdgeOfMap(tr)) {
         return false;
       }
       this.mg
diff --git a/src/core/game/GameImpl.ts b/src/core/game/GameImpl.ts
index 8b9de9b5b..27c721111 100644
--- a/src/core/game/GameImpl.ts
+++ b/src/core/game/GameImpl.ts
@@ -89,6 +89,9 @@ export class GameImpl implements Game {
       this._config.defensePostRange(),
     );
   }
+  isOnEdgeOfMap(ref: TileRef): boolean {
+    return this._map.isOnEdgeOfMap(ref);
+  }
 
   owner(ref: TileRef): Player | TerraNullius {
     return this.playerBySmallID(this.ownerID(ref));
diff --git a/src/core/game/GameMap.ts b/src/core/game/GameMap.ts
index d1c079944..8bf1b8ce2 100644
--- a/src/core/game/GameMap.ts
+++ b/src/core/game/GameMap.ts
@@ -27,6 +27,7 @@ export interface GameMap {
   setOwnerID(ref: TileRef, playerId: number): void;
   hasFallout(ref: TileRef): boolean;
   setFallout(ref: TileRef, value: boolean): void;
+  isOnEdgeOfMap(ref: TileRef): boolean;
   isBorder(ref: TileRef): boolean;
   neighbors(ref: TileRef): TileRef[];
   isWater(ref: TileRef): boolean;
@@ -185,6 +186,12 @@ export class GameMapImpl implements GameMap {
     }
   }
 
+  isOnEdgeOfMap(ref: TileRef): boolean {
+    const x = this.x(ref);
+    const y = this.y(ref);
+    return x == 0 || x == this.width() - 1 || y == 0 || y == this.height() - 1;
+  }
+
   isBorder(ref: TileRef): boolean {
     return this.neighbors(ref).some(
       (tr) => this.ownerID(tr) != this.ownerID(ref),
diff --git a/src/core/game/GameView.ts b/src/core/game/GameView.ts
index ba33c03b3..9370c8895 100644
--- a/src/core/game/GameView.ts
+++ b/src/core/game/GameView.ts
@@ -240,6 +240,9 @@ export class GameView implements GameMap {
     };
     this.defensePostGrid = new DefenseGrid(_map, _config.defensePostRange());
   }
+  isOnEdgeOfMap(ref: TileRef): boolean {
+    return this._map.isOnEdgeOfMap(ref);
+  }
 
   public updatesSinceLastTick(): GameUpdates {
     return this.lastUpdate.updates;