Some 200 mosques in Islam's holiest city, Mecca, point the wrong way for prayers, reports from Saudi Arabia say.
All mosques have a niche showing the direction of the most sacred Islamic site, the Kaaba, an ancient cube-like building in Mecca's Grand Mosque.
But people looking down from recently built high-rises in Mecca found the niches in many older mosques were not pointing directly towards the Kaaba.
Some worshippers are said to be anxious about the validity of their prayers.
There have been suggestions that laser beams could be used to make an exact measurement.
Tawfik al-Sudairy, Islamic affairs ministry deputy secretary, downplayed the problem in remarks quoted by the pan-Arab newspaper al-Hayat.
"There are no major errors but corrections have been made for some old mosques, thanks to modern techniques," he said.
"In any case, it does not affect the prayers."