The number of homes for sale in the U.S. fell 7.1% year-over-year in May, real estate brokerage Redfin reported on Wednesday.

With 1.4 million homes on the market, May represents the lowest number since Redfin began keeping records in 2012.

Redfin attributes this shrinking housing inventory to homeowners feeling trapped by rising mortgage rates, adding that new listings are down 25% to the third lowest level on record.

Additionally, 37% of homes sold in May went for above listing prices, according to Redfin, sparking concerns that this tightened market is fueling bidding wars.