diff --git a/tree_cmd.c b/tree_cmd.c
--- a/tree_cmd.c
+++ b/tree_cmd.c
@@ -139,7 +139,7 @@ int32 CmdPlantTree(int ex, int ey, uint3
 	int32 cost;
 	int sx, sy, x, y;
 
-	if (p2 > MapSize()) return CMD_ERROR;
+	if (p2 >= MapSize()) return CMD_ERROR;
 	/* Check the tree type. It can be random or some valid value within the current climate */
 	if (p1 != (uint)-1 && p1 - _tree_base_by_landscape[_opt.landscape] >= _tree_count_by_landscape[_opt.landscape]) return CMD_ERROR;