diff --git a/tree_cmd.c b/tree_cmd.c
index 174bfd8d62..52a834df08 100644
--- a/tree_cmd.c
+++ b/tree_cmd.c
@@ -493,6 +493,8 @@ static void TileLoop_Trees(TileIndex tile)
 				/* fall through */
 
 			case 2: { /* add a neighbouring tree */
+				byte m3 = _m[tile].m3;
+
 				tile += ToTileIndexDiff(_tileloop_trees_dir[Random() & 7]);
 
 				if (!IsTileType(tile, MP_CLEAR)) return;
@@ -508,6 +510,7 @@ static void TileLoop_Trees(TileIndex tile)
 					default: return;
 				}
 
+				_m[tile].m3 = m3;
 				_m[tile].m4 = 0;
 				SetTileType(tile, MP_TREES);