The Corris Railway Society says that exhibition planned for Y Plas, Machynlleth will not go ahead as planned on August 28 and 29.
It said calling off the exhibition, planned for August 28 and 29, was the safest option because of the risk and likelihood of people grouping around layouts and at trade stands.
However, extra steam trains will operate from Corris Station during the month, allowing visitors to enjoy a relaxed view of the beautiful Dulas Valley.
In addition to the previously advertised Sundays, trains will now run on Saturdays August 7, 14, 21 and 28, plus Bank Holiday Monday, August 30. Trains will leave Corris station at 11am, 1pm and 3pm and tickets must be pre-booked online via corris.co.uk.
The railway is also accepting bookings, subject to volunteer staff availability, for its "Your Railway for the Day" package. Groups of up to six people, or even individuals, can drive steam, diesel or battery electric locomotives, work with the guard and the signalman and enjoy exclusive use of the railway.