This must have really been something to taco ‘bout.

An Indiana librarian tweeted that she found the most unusual bookmark between the pages of a book dropped off at her library — an entire taco.

“Don’t have a bookmark?” Amanda Monson tweeted on Thursday. “Try using a taco. (Actual photo of an actual book found in the book drop at my library in Indiana a few years back).”

Monson, who works at the LaPorte County Library, told Inside Edition Monday that the book was not one of the library’s own, but a donation.

“The staff took a photo of it and threw the book away,” she said.

Monson did not mention the name of the book, but another Twitter user suggested that it was “Nonsense Songs and Stories,” illustrated by Edward Lear.

Monson’s tweet comes in the midst of a viral “Don’t have a bookmark?” joke on social media — in which actual food and drink companies have shared images of their products wedged between the pages of a book.

Chex Mix started the trend early last week, prompting SparkNotes to reply, “We’re calling the cops.”

Since then, Oreo, Vitamin Water, Gushers and others have jumped on the bandwagon.

The Big Apple’s Strand bookstore clearly didn’t find the trend amusing.

“Don’t have a bookmark?” the bookstore said in a Thursday tweet. “Use literally ANYTHING BUT FOOD OR DRINK, YOU MONSTERS @ChexMix @vitaminwater.”

“This is the worst social media challenge in history and we demand that all of you stop it AT ONCE,” publishing company Random House chimed in. “Books are precious objects that deserve our respect. Now go sit in the corner and think about what you’ve done in the name of ‘content.’”

Monson, who started working as a librarian seven years ago, told Inside Edition she’s seen odd objects ranging from uncashed paychecks to panty liners between the pages of returned books.

“You can ask any public librarian, and they will have stories about the weird things that get left in books and returned to us,” she said.