Wal-Mart on Thursday reported slower sales growth at its U.S. stores during the holiday quarter.

The 0.6 percent increase in sales at U.S. stores open more than a year marks the chain’s sixth straight three-month period of growth after a long run of decreases.

And yet the gain is a relatively modest one, especially compared to the 1.5 percent growth it experienced in the same period last year, underscoring the challenges Wal-Mart faces as it tries to win over customers with cleaner, better-stocked stores and a more competitive digital offering.

Wal-Mart lowered its revenue forecast for the year, saying it now expects to see flat sales instead of 3 to 4 percent growth. The chain said the change in expectations is because of the continued strength of the U.S. dollar and the impact of the decision it announced it January to close 269 of its stores across the globe. This more muted guidance is likely a key reason why its stock fell nearly 5 percent in early trading.

Wal-Mart has been ramping up its efforts in the last year to become a more serious rival in e-commerce to Amazon.com. It has rapidly expanded to 20 metropolitan areas a service that allows customers to buy groceries online and pick them up curbside at a Wal-Mart store. It is testing Shipping Pass, an Amazon Prime-like program that would offer shoppers unlimited three-day shipping on their orders. Wal-Mart even tried to steal some of Amazon’s thunder on the Seattle company’s Prime Day deals bonanza, launching a rival online sale of its own.