diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index f471af2..d3e8c94 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -1521,6 +1521,8 @@ CommandCost CmdConvertRail(TileIndex tile, DoCommandFlag flags, uint32 p1, uint3
 
 	TrainList affected_trains;
 
+	SmallVector<TileIndex, 8> seen_tunnel_bridges;
+
 	CommandCost cost(EXPENSES_CONSTRUCTION);
 	CommandCost error = CommandCost(STR_ERROR_NO_SUITABLE_RAILROAD_TRACK); // by default, there is no track to convert.
 	TileArea ta(tile, p1);
@@ -1637,11 +1639,6 @@ CommandCost CmdConvertRail(TileIndex tile, DoCommandFlag flags, uint32 p1, uint3
 			case MP_TUNNELBRIDGE: {
 				TileIndex endtile = GetOtherTunnelBridgeEnd(tile);
 
-				/* If both ends of tunnel/bridge are in the range, do not try to convert twice -
-				 * it would cause assert because of different test and exec runs */
-				if (endtile < tile && TileX(endtile) >= TileX(ta.tile) && TileX(endtile) < TileX(ta.tile) + ta.w &&
-						TileY(endtile) >= TileY(ta.tile) && TileY(endtile) < TileY(ta.tile) + ta.h) continue;
-
 				/* When not converting rail <-> el. rail, any vehicle cannot be in tunnel/bridge */
 				if (!IsCompatibleRail(GetRailType(tile), totype)) {
 					CommandCost ret = TunnelBridgeIsFree(tile, endtile);
@@ -1686,6 +1683,12 @@ CommandCost CmdConvertRail(TileIndex tile, DoCommandFlag flags, uint32 p1, uint3
 						TileIndex t = tile + delta;
 						for (; t != endtile; t += delta) MarkTileDirtyByTile(t); // TODO encapsulate this into a function
 					}
+				} else {
+					/* If both ends of tunnel/bridge are in the range, do not try to convert twice -
+					 * it would cause assert because of different test and exec runs */
+					if (seen_tunnel_bridges.Contains(endtile))
+						continue;
+					*(seen_tunnel_bridges.Append()) = tile;
 				}
 
 				cost.AddCost((GetTunnelBridgeLength(tile, endtile) + 2) * RailConvertCost(type, totype));