The tech giant on Friday announced that it has raised the monthly Amazon Prime membership rate from $10.99 per month to $12.99 per month, an increase of 18%. Amazon was quick to note, however, that the $99 annual membership fee for Amazon Prime will remain the same. Students who were paying $5.49 per month for access to Prime will now be charged $6.49.

Amazon Prime is one of the company’s most important offerings. Subscribers get access to free two-day shipping on millions of products, as well as discounted rates on next-day shipping. Amazon Prime subscriptions also include access to the company’s suite of streaming services, including Prime Video, Prime Music, and more.

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Traditionally, Prime has been an annual subscription, but in 2016, Amazon unveiled its monthly plan to attract more members to the program. The move allowed those who couldn’t afford Prime to take advantage of the benefits, and also offered some flexibility in deciding how and when to use it.

Amazon doesn’t break out its Prime membership by annual and monthly members, so it’s unknown how many people will be affected by the change. If nothing else, it could provoke some monthly payers to consider an annual membership. By signing up for Prime’s annual plan, users pay just $99. The new monthly rate will cost members about $156 for the year.

Amazon did not immediately respond to a Fortune request for comment on the move.