diff --git a/landscape.c b/landscape.c
index 881ca67a14..1f5cffddb1 100644
--- a/landscape.c
+++ b/landscape.c
@@ -451,7 +451,7 @@ void ConvertGroundTilesIntoWaterTiles(void)
 		if (IsTileType(tile, MP_CLEAR) && GetTileSlope(tile, &h) == 0 && h == 0) {
 			SetTileType(tile, MP_WATER);
 			_map5[tile] = 0;
-			_map_owner[tile] = OWNER_WATER;
+			SetTileOwner(tile, OWNER_WATER);
 		}
 	}
 }
diff --git a/openttd.c b/openttd.c
index ffd159aa39..c1205eda39 100644
--- a/openttd.c
+++ b/openttd.c
@@ -1188,11 +1188,9 @@ static void ConvertTownOwner(void)
 			if ((_map5[tile] & 0xF0) == 0x10 && _map3_lo[tile] & 0x80)
 				_map3_lo[tile] = OWNER_TOWN;
 
-			if (_map_owner[tile] & 0x80)
-				_map_owner[tile] = OWNER_TOWN;
+			if (_map_owner[tile] & 0x80) SetTileOwner(tile, OWNER_TOWN);
 		} else if (IsTileType(tile, MP_TUNNELBRIDGE)) {
-			if (_map_owner[tile] & 0x80)
-				_map_owner[tile] = OWNER_TOWN;
+			if (_map_owner[tile] & 0x80) SetTileOwner(tile, OWNER_TOWN);
 		}
 	}
 }
@@ -1300,7 +1298,7 @@ bool AfterLoadGame(uint version)
 
 		BEGIN_TILE_LOOP(tile_cur, w, h, tile)
 			if (IsTileType(tile_cur, MP_WATER) && GetTileOwner(tile_cur) >= MAX_PLAYERS)
-				_map_owner[tile_cur] = OWNER_WATER;
+				SetTileOwner(tile_cur, OWNER_WATER);
 		END_TILE_LOOP(tile_cur, w, h, tile)
 	}
 
diff --git a/rail_cmd.c b/rail_cmd.c
index 7459b37ac8..0b6a8fc92a 100644
--- a/rail_cmd.c
+++ b/rail_cmd.c
@@ -316,7 +316,7 @@ int32 CmdBuildSingleRail(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 					cost += ret;
 
 					if (flags & DC_EXEC) {
-						_map_owner[tile] = _current_player;
+						SetTileOwner(tile, _current_player);
 						_map3_lo[tile] &= ~0x0F;
 						_map3_lo[tile] |= p1;
 						_map5[tile] = (m5 & 0xC7) | 0x20; // railroad under bridge
@@ -365,7 +365,7 @@ int32 CmdBuildSingleRail(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 					)) {
 				if (flags & DC_EXEC) {
 					_map3_lo[tile] = GetTileOwner(tile);
-					_map_owner[tile] = _current_player;
+					SetTileOwner(tile, _current_player);
 					_map3_hi[tile] = p1;
 					_map5[tile] = 0x10 | (rail_bit == 1 ? 0x08 : 0x00); // level crossing
 				}
@@ -387,7 +387,7 @@ int32 CmdBuildSingleRail(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 
 			if (flags & DC_EXEC) {
 				SetTileType(tile, MP_RAILWAY);
-				_map_owner[tile] = _current_player;
+				SetTileOwner(tile, _current_player);
 				_map2[tile] = 0; // Bare land
 				_map3_lo[tile] = p1; // No signals, rail type
 				_map5[tile] = rail_bit;
@@ -461,7 +461,7 @@ int32 CmdRemoveSingleRail(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 		if (!(flags & DC_EXEC))
 			return _price.remove_rail;
 
-		_map_owner[tile] = OWNER_NONE;
+		SetTileOwner(tile, OWNER_NONE);
 		_map5[tile] = ti.map5 & 0xC7;
 	} else if (ti.type == MP_STREET) {
 		byte m5;
@@ -485,7 +485,7 @@ int32 CmdRemoveSingleRail(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 			return _price.remove_rail;
 
 		_map5[tile] = m5;
-		_map_owner[tile] = _map3_lo[tile];
+		SetTileOwner(tile, _map3_lo[tile]);
 		_map2[tile] = 0;
 	} else {
 		assert(ti.type == MP_RAILWAY);
@@ -2028,7 +2028,7 @@ static void ChangeTileOwner_Track(uint tile, byte old_player, byte new_player)
 	if (!IsTileOwner(tile, old_player)) return;
 
 	if (new_player != 255) {
-		_map_owner[tile] = new_player;
+		SetTileOwner(tile, new_player);
 	}	else {
 		DoCommandByTile(tile, 0, 0, DC_EXEC, CMD_LANDSCAPE_CLEAR);
 	}
diff --git a/road_cmd.c b/road_cmd.c
index 26c96badee..f48fb44612 100644
--- a/road_cmd.c
+++ b/road_cmd.c
@@ -195,7 +195,7 @@ int32 CmdRemoveRoad(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 		if (flags & DC_EXEC) {
 			ChangeTownRating(t, -road_remove_cost[(byte)edge_road], RATING_ROAD_MINIMUM);
 			_map5[tile] = ti.map5 & 0xC7;
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 			MarkTileDirtyByTile(tile);
 		}
 		return cost;
@@ -470,7 +470,7 @@ do_clear:;
 			SetTileType(tile, MP_STREET);
 			_map5[tile] = 0;
 			_map2[tile] = p2;
-			_map_owner[tile] = _current_player;
+			SetTileOwner(tile, _current_player);
 		}
 
 		_map5[tile] |= (byte)pieces;
@@ -1148,14 +1148,14 @@ static void ChangeTileOwner_Road(uint tile, byte old_player, byte new_player)
 	if (!IsTileOwner(tile, old_player)) return;
 
 	if (new_player != 255) {
-		_map_owner[tile] = new_player;
+		SetTileOwner(tile, new_player);
 	}	else {
 		b = _map5[tile]&0xF0;
 		if (b == 0) {
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 		} else if (b == 0x10) {
 			_map5[tile] = (_map5[tile]&8) ? 0x5 : 0xA;
-			_map_owner[tile] = _map3_lo[tile];
+			SetTileOwner(tile, _map3_lo[tile]);
 			_map3_lo[tile] = 0;
 			_map3_hi[tile] &= 0x80;
 		} else {
diff --git a/station_cmd.c b/station_cmd.c
index 1721e38e06..4876b896f4 100644
--- a/station_cmd.c
+++ b/station_cmd.c
@@ -2827,7 +2827,7 @@ void BuildOilRig(uint tile)
 
 			SetTileType(tile, MP_STATION);
 			_map5[tile] = 0x4B;
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 			_map3_lo[tile] = 0;
 			_map3_hi[tile] = 0;
 			_map2[tile] = st->index;
@@ -2884,7 +2884,7 @@ static void ChangeTileOwner_Station(uint tile, byte old_player, byte new_player)
 
 	if (new_player != 255) {
 		Station *st = GetStation(_map2[tile]);
-		_map_owner[tile] = new_player;
+		SetTileOwner(tile, new_player);
 		st->owner = new_player;
 		_global_station_sort_dirty = true; // transfer ownership of station to another player
 		InvalidateWindowClasses(WC_STATION_LIST);
diff --git a/tile.h b/tile.h
index e19a24b7f4..1d8cd094ac 100644
--- a/tile.h
+++ b/tile.h
@@ -88,6 +88,16 @@ static inline Owner GetTileOwner(TileIndex tile)
 	return _map_owner[tile];
 }
 
+static inline void SetTileOwner(TileIndex tile, Owner owner)
+{
+	assert(tile < MapSize());
+	assert(!IsTileType(tile, MP_HOUSE));
+	assert(!IsTileType(tile, MP_VOID));
+	assert(!IsTileType(tile, MP_INDUSTRY));
+
+	_map_owner[tile] = owner;
+}
+
 static inline bool IsTileOwner(TileIndex tile, Owner owner)
 {
 	return GetTileOwner(tile) == owner;
diff --git a/town_cmd.c b/town_cmd.c
index cea3489096..4b13be7b68 100644
--- a/town_cmd.c
+++ b/town_cmd.c
@@ -746,7 +746,7 @@ static int GrowTownAtRoad(Town *t, uint tile)
 			else if (_game_mode == GM_EDITOR) {
 				/* If we are in the SE, and this road-piece has no town owner yet, it just found an
 				*  owner :) (happy happy happy road now) */
-				_map_owner[tile] = OWNER_TOWN;
+				SetTileOwner(tile, OWNER_TOWN);
 				_map2[tile] = t->index;
 			}
 		}
diff --git a/tree_cmd.c b/tree_cmd.c
index e4fe68ffc7..52856fe690 100644
--- a/tree_cmd.c
+++ b/tree_cmd.c
@@ -580,7 +580,7 @@ static void TileLoop_Trees(uint tile)
 				if ((m2&0x30) != 0x20) // if not on snow/desert, then on rough land
 					m5 = 7;
 			}
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 		}
 	} else {
 		/* in the middle of a transition, change to next */
diff --git a/tunnelbridge_cmd.c b/tunnelbridge_cmd.c
index 7460f7b6e3..1aa5a49358 100644
--- a/tunnelbridge_cmd.c
+++ b/tunnelbridge_cmd.c
@@ -711,7 +711,7 @@ static int32 DoClearBridge(uint tile, uint32 flags)
 
 		if (flags & DC_EXEC) {
 			_map5[tile] = _map5[tile] & ~0x38;
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 			MarkTileDirtyByTile(tile);
 		}
 		return cost;
@@ -726,7 +726,7 @@ static int32 DoClearBridge(uint tile, uint32 flags)
 		cost = _price.clear_water;
 		if (flags & DC_EXEC) {
 			_map5[tile] = _map5[tile] & ~0x38;
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 			MarkTileDirtyByTile(tile);
 		}
 		return cost;
@@ -1373,7 +1373,7 @@ static void ChangeTileOwner_TunnelBridge(uint tile, byte old_player, byte new_pl
 	if (!IsTileOwner(tile, old_player)) return;
 
 	if (new_player != 255) {
-		_map_owner[tile] = new_player;
+		SetTileOwner(tile, new_player);
 	}	else {
 		if((_map5[tile] & 0xC0)==0xC0) {
 			// the stuff BELOW the middle part is owned by the deleted player.
@@ -1382,7 +1382,7 @@ static void ChangeTileOwner_TunnelBridge(uint tile, byte old_player, byte new_pl
 				_map5[tile] &= ~(1 << 5 | 1 << 4 | 1 << 3); // no transport route under bridge anymore..
 			} else {
 				// for road, change the owner of the road to local authority
-				_map_owner[tile] = OWNER_NONE;
+				SetTileOwner(tile, OWNER_NONE);
 			}
 		} else {
 			DoCommandByTile(tile, 0, 0, DC_EXEC, CMD_LANDSCAPE_CLEAR);
diff --git a/unmovable_cmd.c b/unmovable_cmd.c
index b1a94e1675..e7673c599d 100644
--- a/unmovable_cmd.c
+++ b/unmovable_cmd.c
@@ -358,7 +358,7 @@ void GenerateUnmovables(void)
 				continue;
 			SetTileType(tile, MP_UNMOVABLE);
 			_map5[tile] = 0;
-			_map_owner[tile] = OWNER_NONE;
+			SetTileOwner(tile, OWNER_NONE);
 			if (--j == 0)
 				break;
 		}
@@ -390,7 +390,7 @@ restart:
 
 		SetTileType(tile, MP_UNMOVABLE);
 		_map5[tile] = 1;
-		_map_owner[tile] = OWNER_NONE;
+		SetTileOwner(tile, OWNER_NONE);
 	} while (--i);
 }
 
@@ -399,7 +399,7 @@ static void ChangeTileOwner_Unmovable(uint tile, byte old_player, byte new_playe
 	if (!IsTileOwner(tile, old_player)) return;
 
 	if (_map5[tile]==3 && new_player != 255) {
-		_map_owner[tile] = new_player;
+		SetTileOwner(tile, new_player);
 	}	else {
 		DoClearSquare(tile);
 	}
diff --git a/water_cmd.c b/water_cmd.c
index 5c476f8c66..31bbb70fa2 100644
--- a/water_cmd.c
+++ b/water_cmd.c
@@ -689,7 +689,7 @@ static void ChangeTileOwner_Water(uint tile, byte old_player, byte new_player)
 	if (!IsTileOwner(tile, old_player)) return;
 
 	if (new_player != 255) {
-		_map_owner[tile] = new_player;
+		SetTileOwner(tile, new_player);
 	} else {
 		DoCommandByTile(tile, 0, 0, DC_EXEC, CMD_LANDSCAPE_CLEAR);
 	}