Laser interferometers provide an easy path for traceable measurements as most commercial instruments are inherently accurate to better than 10-7. The main problem with using these interferometers over an extended path can be the alignment requirements which can only be met with a precision rail system. Tape benches are typically 50 m (or more) long and are easily affected by building movement, requiring frequent re-alignment. An interferometer with an expanded measurement beam has significantly reduced alignment requirements and one with a beam diameter of 45 mm was used by the author to measure survey pillars. This had an alignment tolerance of +/- 10 mm allowing the use of a simple stretched wire rail system. This paper describes a simple adaptation that can be made to a commercial interferometer to expand the measurement beam without interfering with its normal operation.