In-N-Out Burger closed all 37 of its Texas restaurants Monday and Tuesday due to an undisclosed issue with buns, the company said.

“At In-N-Out Burgers, we have always served the highest quality food with no compromise. We recently discovered that our buns in Texas do not meet the quality standards that we demand,” Bob Lang, Jr., executive vice president of the chain, told Business Insider.

In-N-Out did not say what the issue was exactly. The brand’s Texas units are supplied by In-N-Out’s Dallas distribution center. Lang said the chain closed so it could “serve our normal high-quality bun,” and that new buns are on the way, with stores expected to reopen Wednesday.

The Irvine, California-based chain has locations in California, Arizona, Nevada, Oregon, Texas, and Utah. When In-N-Out opened a distribution center in the Dallas area in 2011, it opened stores in major metros such as Austin and San Antonio so that it could keep a close eye on quality control. The company has roughly 320 units with estimated sales over $600 million.

In-N-Out also has plans to expand into Colorado in the coming years, and is working on plans to build a patty production facility and distribution center in Colorado Springs. No exact timeline has been shared.

It opened its first restaurants in Arizona in 2000, Utah in 2008, Texas in 2011, and Oregon in 2015.