A washing machine and a method of controlling a washing machine are provided. The washing machine may include a drum in which laundry is provided and is rotated. The drum may operate at a first speed such that part of the laundry tumbles within the drum and another part of the laundry adheres to the drum. An unbalance amount or a first speed operation time of the drum, which is detected when the drum operates at the first speed, may be determined. When an abnormality occurs, rotation of the drum may stop or decelerate. Accordingly, at the time of a dehydration cycle, stability of the washing machine and laundry balancing can be ensured.