diff --git a/clear_cmd.c b/clear_cmd.c
--- a/clear_cmd.c
+++ b/clear_cmd.c
@@ -233,7 +233,7 @@ int32 CmdTerraformLand(int x, int y, uin
 	tile = TileVirtXY(x, y);
 
 	/* Make an extra check for map-bounds cause we add tiles to the originating tile */
-	if (tile + TileDiffXY(1, 1) > MapSize()) return CMD_ERROR;
+	if (tile + TileDiffXY(1, 1) >= MapSize()) return CMD_ERROR;
 
 	if (p1 & 1) {
 		if (!TerraformTileHeight(&ts, tile + TileDiffXY(1, 0),
@@ -332,7 +332,7 @@ int32 CmdLevelLand(int ex, int ey, uint3
 	TileIndex tile;
 	int32 ret, cost, money;
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	SET_EXPENSES_TYPE(EXPENSES_CONSTRUCTION);
 
diff --git a/landscape.c b/landscape.c
--- a/landscape.c
+++ b/landscape.c
@@ -307,7 +307,7 @@ int32 CmdClearArea(int ex, int ey, uint3
 	int x,y;
 	bool success = false;
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	SET_EXPENSES_TYPE(EXPENSES_CONSTRUCTION);
 
diff --git a/rail_cmd.c b/rail_cmd.c
--- a/rail_cmd.c
+++ b/rail_cmd.c
@@ -566,7 +566,7 @@ static int32 CmdRailTrackHelper(int x, i
 	RailType railtype = (RailType)GB(p2, 0, 4);
 
 	if (!ValParamRailtype(railtype) || !ValParamTrackOrientation(track)) return CMD_ERROR;
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 	trackdir = TrackToTrackdir(track);
 
 	/* unpack end point */
@@ -829,7 +829,7 @@ static int32 CmdSignalTrackHelper(int x,
 	byte semaphores = (HASBIT(p2, 3)) ? 8 : 0;
 	byte signal_density = (p2 >> 24);
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 	if (signal_density == 0 || signal_density > 20) return CMD_ERROR;
 
 	if (!IsTileType(tile, MP_RAILWAY)) return CMD_ERROR;
@@ -988,7 +988,7 @@ int32 CmdConvertRail(int ex, int ey, uin
 	SET_EXPENSES_TYPE(EXPENSES_CONSTRUCTION);
 
 	if (!ValParamRailtype(p2)) return CMD_ERROR;
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	// make sure sx,sy are smaller than ex,ey
 	sx = TileX(p1) * TILE_SIZE;
diff --git a/road_cmd.c b/road_cmd.c
--- a/road_cmd.c
+++ b/road_cmd.c
@@ -518,7 +518,7 @@ int32 CmdBuildLongRoad(int x, int y, uin
 
 	SET_EXPENSES_TYPE(EXPENSES_CONSTRUCTION);
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	start_tile = p1;
 	end_tile = TileVirtXY(x, y);
@@ -573,7 +573,7 @@ int32 CmdRemoveLongRoad(int x, int y, ui
 
 	SET_EXPENSES_TYPE(EXPENSES_CONSTRUCTION);
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	start_tile = p1;
 	end_tile = TileVirtXY(x, y);
diff --git a/tunnelbridge_cmd.c b/tunnelbridge_cmd.c
--- a/tunnelbridge_cmd.c
+++ b/tunnelbridge_cmd.c
@@ -209,7 +209,7 @@ int32 CmdBuildBridge(int x, int y, uint3
 	bridge_type = GB(p2, 0, 8);
 	railtype    = GB(p2, 8, 8);
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	// type of bridge
 	if (HASBIT(railtype, 7)) { // bit 15 of original p2 param
diff --git a/water_cmd.c b/water_cmd.c
--- a/water_cmd.c
+++ b/water_cmd.c
@@ -215,7 +215,7 @@ int32 CmdBuildCanal(int x, int y, uint32
 	int size_x, size_y;
 	int sx, sy;
 
-	if (p1 > MapSize()) return CMD_ERROR;
+	if (p1 >= MapSize()) return CMD_ERROR;
 
 	sx = TileX(p1);
 	sy = TileY(p1);