Boo Boo the Chihuahua is the world smallest dog.

At just four inches tall, the diminutive dog in Raceland, Kentucky now has the very big title of smallest in the world. The Guinness Book of World Records made it official.

Lana Elswick says her Chihuahua Boo-Boo was born the size of her thumb. Elswick says from the beginning she knew her dog was special, but it wasn’t until a few weeks ago that she knew just how special.

The Guinness Book now considers the full-grown though petite pet the smallest dog in the world, nearly an inch smaller than the previous record holder.