File this under "things that will restore your faith in humanity." After forgetting to adequately tip a waitress, a customer snail-mailed her an extra $15. Yes, really.

Sarah, who goes by dior_show on Reddit, posted the letter that came with the cash, writing, "My friend is a waitress and this letter was sent to the restaurant addressed to her."

"I was in for dinner last Friday night," the apologetic customer wrote. "I miscalculated your tip and ended up shortchanging you. I left you $16.50 on a $132.30 bill. … I am so sorry — it was purely an oversight."

$16.50 is a 12% tip; $31.50 (the customer's original shoddy tip plus the mailed $15) is 24%, a more reasonable amount for the "great meal" and "perfect service" the family enjoyed at the Boston restaurant.

"My friend said she sees so many horror stories in the service industry that she just couldn't believe this was real when she got it," Sarah told Mashable via email. "She thought it was such a kind gesture. She is a sweetheart, and a great waitress. I personally wanted to share the story because I feel that good deeds often go unnoticed. It's great to see people going out of their way to be kind to one another." 🙌

H/T Mashable