diff --git a/gtfs/spec/en/reference.md b/gtfs/spec/en/reference.md
index 164a9a80..cb905621 100644
--- a/gtfs/spec/en/reference.md
+++ b/gtfs/spec/en/reference.md
@@ -694,7 +694,7 @@ For a given ordered pair of arriving trip and departing trip, the transfer with
 | `from_trip_id`  | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes begins.<br><br>If `from_trip_id` is defined, the transfer will apply to the arriving trip for the given `from_stop_id`.<br><br>If both `from_trip_id` and `from_route_id` are defined, the `trip_id` must belong to the `route_id`, and `from_trip_id` will take precedence.<br><br>Conditionally Required:<br>- **Required** if `transfer_type` is `4` or `5`. <br>- Optional otherwise. |
 | `to_trip_id`  | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes ends.<br><br>If `to_trip_id` is defined, the transfer will apply to the departing trip for the given `to_stop_id`.<br><br>If both `to_trip_id` and `to_route_id` are defined, the `trip_id` must belong to the `route_id`, and `to_trip_id` will take precedence. <br><br>Conditionally Required:<br>- **Required** if `transfer_type` is `4` or `5`. <br>- Optional otherwise. |
 |  `transfer_type` | Enum | **Required** | Indicates the type of connection for the specified (`from_stop_id`, `to_stop_id`) pair. Valid options are:<br><br> `0` or empty - Recommended transfer point between routes.<br>`1` - Timed transfer point between two routes. The departing vehicle is expected to wait for the arriving one and leave sufficient time for a rider to transfer between routes.<br>`2` - Transfer requires a minimum amount of time between arrival and departure to ensure a connection. The time required to transfer is specified by `min_transfer_time`.<br>`3` - Transfers are not possible between routes at the location.<br>`4` - Passengers can transfer from one trip to another by staying onboard the same vehicle (an "in-seat transfer"). More details about this type of transfer [below](#linked-trips).  <br>`5` - In-seat transfers are not allowed between sequential trips. The passenger must alight from the vehicle and re-board. More details about this type of transfer [below](#linked-trips). |
-|  `min_transfer_time` | Non-negative integer | Optional | Amount of time, in seconds, that must be available to permit a transfer between routes at the specified stops. The `min_transfer_time` should be sufficient to permit a typical rider to move between the two stops, including buffer time to allow for schedule variance on each route. |
+|  `min_transfer_time` | Non-negative integer | **Conditionally Required** | Amount of time, in seconds, that must be available to permit a transfer between routes at the specified stops. The `min_transfer_time` should be sufficient to permit a typical rider to move between the two stops, including buffer time to allow for schedule variance on each route. <br><br>Conditionally Required:<br>- **Required** if `transfer_type` is `2`. <br>- Optional otherwise. |
 
 #### Linked trips