diff --git a/src/client/view/GameView.ts b/src/client/view/GameView.ts
index 6dd2d9fcc..283e571b3 100644
--- a/src/client/view/GameView.ts
+++ b/src/client/view/GameView.ts
@@ -76,6 +76,8 @@ export class GameView implements GameMap {
     import("../render/types").PlayerState
   >();
   private _unitStates = new Map<number, import("../render/types").UnitState>();
+  /** smallID → team, for the renderer's relation matrix (team games). */
+  private _teams = new Map<number, string>();
   private updatedTiles: TileRef[] = [];
   private updatedTerrainTiles: TileRef[] = [];
 
@@ -327,6 +329,10 @@ export class GameView implements GameMap {
         );
         this._players.set(pu.id, player);
         this._playerStates.set(pu.smallID!, player.state);
+        const team = player.team();
+        if (team !== null) {
+          this._teams.set(pu.smallID!, team);
+        }
       }
     });
 
@@ -472,7 +478,7 @@ export class GameView implements GameMap {
       isTransitiveTarget: (sid) =>
         this._myPlayer?.hasTransitiveTarget(sid) ?? false,
     });
-    const rel = buildRelationMatrix(this._playerStates);
+    const rel = buildRelationMatrix(this._playerStates, this._teams);
     f.relationMatrix = rel.matrix;
     f.relationSize = rel.size;
     f.allianceClusters = computeAllianceClusters(this._playerStates);
diff --git a/tests/client/view/GameView.test.ts b/tests/client/view/GameView.test.ts
index 6ed1c1f72..f520aba9f 100644
--- a/tests/client/view/GameView.test.ts
+++ b/tests/client/view/GameView.test.ts
@@ -466,4 +466,24 @@ describe("GameView.frameData() — renderer contract", () => {
     game.update(makeEmptyGu(2));
     expect(game.frameData().structuresDirty).toBe(false);
   });
+
+  it("frame.relationMatrix marks same-team players as friendly (team games)", () => {
+    const RELATION_FRIENDLY = 1;
+    const RELATION_NEUTRAL = 0;
+    const game = makeGameView();
+    game.update(
+      withPlayers(1, [
+        makePlayerUpdate({ id: "alice", smallID: 1, team: "red" }),
+        makePlayerUpdate({ id: "bob", smallID: 2, team: "red" }),
+        makePlayerUpdate({ id: "carol", smallID: 3, team: "blue" }),
+      ]),
+    );
+    const { relationMatrix, relationSize } = game.frameData();
+    // Teammates (no explicit alliance) are friendly both ways.
+    expect(relationMatrix[1 * relationSize + 2]).toBe(RELATION_FRIENDLY);
+    expect(relationMatrix[2 * relationSize + 1]).toBe(RELATION_FRIENDLY);
+    // Cross-team players stay neutral.
+    expect(relationMatrix[1 * relationSize + 3]).toBe(RELATION_NEUTRAL);
+    expect(relationMatrix[3 * relationSize + 1]).toBe(RELATION_NEUTRAL);
+  });
 });