WASHINGTON (AP) — U.S. wholesale companies added modestly to their stockpiles in May. But their sales dropped by the largest amount in three years, a troubling sign for future growth.

The Commerce Department says wholesale stockpiles rose 0.3 percent in May. That followed a 0.5 percent increase in April, which was revised lower from an initially reported 1.1 percent gain.

But sales at the wholesale level fell 0.8 percent in May, the biggest decline since March 2009.

Greater restocking means companies ordered more goods, which increases factory production. But the broader economic benefits from faster restocking will likely be offset by the decline in sales.

Stockpiles at the wholesale level stood at $484.1 billion in May. That is 25.8 percent above the post-recession low of $384.9 billion in September 2009.