While demand for COVID-19 vaccinations is surging, appointment no-shows and unexpected supplies could leave providers with extra doses. To prevent waste, some pharmacies, including Walmart and CVS, are assembling customer wait lists along with plans to vaccinate their employees with excess shots.

Various state and local rules dictate who may receive vaccinations first. Some people eager for inoculation are signing up for multiple wait lists, leading to possible overbookings, missed slots, and unclaimed shots that can expire if not used within hours of leaving cold storage.

CVS and Walgreens have already begun vaccinating employees using leftover doses that are set to expire, the companies tell the Wall Street Journal. They plan to continue the practice, including giving shots to workers who might not otherwise qualify for vaccination, rather than see shots thrown away, they tell the Journal.

“Surplus doses have been, and will continue to be, minimal given the appointment system; in other words, we know what we need at each store,” T.J. Crawford, a spokesperson for CVS, told Fortune. “In the rare instances where we do have expiring doses, we reach out to employees and customers who qualify.  If we’re not able to locate anyone from eligible populations, we’ll make sure no dose goes to waste by vaccinating on-site employees.”

Walmart is also offering spare doses that are at risk of spoiling to both customers and workers. Initially, they look for people who qualify under the regulations of that state. If no one eligible is available, when allowed, they move down their lists to lower-priority groups.

Some stores are keeping lists of eligible people to call to give spare doses, says the Journal. And some stores are making last-minute announcements to in-store shoppers over their loudspeaker systems.

The federal government is set to begin sending 1 million doses of the vaccines to 6,500 pharmacies around the country, including drugstores and grocers, starting Thursday.

The issue of how to handle excess doses has taken center stage recently, especially after news that a Texas doctor was fired from his government job and charged with stealing 10 vaccine doses after he distributed the vaccine from an open vial that would have gone bad in six hours to people outside a scheduled event.