diff --git a/command.c b/command.c
--- a/command.c
+++ b/command.c
@@ -177,6 +177,7 @@ static CommandProc * const _command_proc
 	CmdBuildSingleSignal,					/* 8  */
 	CmdRemoveSingleSignal,				/* 9  */
 	CmdTerraformLand,							/* 10 */
+	/***************************************************/
 	CmdPurchaseLandArea,					/* 11 */
 	CmdSellLandArea,							/* 12 */
 	CmdBuildTunnel,								/* 13 */
@@ -331,6 +332,9 @@ int32 DoCommand(int x, int y, uint32 p1,
 	int32 res;
 	CommandProc *proc;
 
+	/* Do not even think about executing out-of-bounds tile-commands */
+	if (TILE_FROM_XY(x,y) > MapSize()) return CMD_ERROR;
+
 	proc = _command_proc_table[procc];
 
 	if (_docommand_recursive == 0) {
@@ -399,6 +403,9 @@ bool DoCommandP(TileIndex tile, uint32 p
 	int x = TileX(tile) * 16;
 	int y = TileY(tile) * 16;
 
+	/* Do not even think about executing out-of-bounds tile-commands */
+	if (tile > MapSize()) return false;
+
 	assert(_docommand_recursive == 0);
 
 	_error_message = INVALID_STRING_ID;