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When Walmart (wmt, +1.02%) reported on Thursday that comparable sales at its U.S. stores had risen in the first quarter, its stock rose the most in eight years in a relief rally.

After a week of dismal earnings reports by many retailers, investors were just glad to see that Walmart had been able to attract more shoppers to its stores for the sixth straight quarter in its biggest market and build sales for the eighth quarter. (It says a lot about the state of retail that Wall Street got so excited over a 1% gain.)

But amid the signs of progress was a data point that normally would give Wal-Mart Stores investors pause: e-commerce sales rose only 7% in the quarter, slowing down yet again and suggesting the retailer is struggling to keep pace with Amazon.com (amzn, +0.12%).

“Growth here is too slow,” Walmart CEO Doug McMillon said on pre-recorded call.

According to recent data from eMarketer, Walmart is the second largest U.S. online retailer, with $12.5 billion in sales in the last year (the figure is $13.5 billion globally) But that is a far cry from the $82.8 billion Amazon pulled in. What’s more, Walmart’s digital growth is well below the economy-wide rate of 15.1% in the first quarter, according to the U.S. Department of Commerce. E-commerce accounts for about 3% of Walmart sales, compared to 7.8% across retail.

Some of the sluggishness comes from customers not yet knowing how much they can buy on walmart.com, something McMillon said would change. (Walmart now offers 10…