Police are carrying out enquiries after the incident in Church Brampton on Wednesday, 22 June.
A woman was walking her dog in fields at the end of Golf Lane, at about 4pm, when a man whistled at her.
When she turned to see who was whistling, the man indecently exposed himself, at which point the victim ran off.
The offender was a white man, of slim build, 5ft 9 inches, with short brown hair. He was wearing sunglasses, a blue top and blue jeans.
Witnesses or anyone with information about this incident can contact police on 101 or Crimestoppers anonymously on 0800 555 111.