The 19-year-old aspiring actress dedicated a post to the Home Alone star on Instagram Stories while ringing in his birthday Saturday.
"HAPPY BURFDAY I LOVE U," she captioned a throwback photo of herself with Culkin. "Make 37 your [expletive]."
Culkin thanked his friends and fans for their birthday wishes in a tweet the next day, writing, "Thank you all for bday wishes! You all are amazing!"
Culkin is also godfather to Jackson's brothers, 20-year-old Prince Jackson and 15-year-old Blanket Jackson. He was close friends with the siblings' late dad, Michael Jackson, up until the singer's death at age 50 in 2009.
Jackson and Culkin celebrated their bond by getting matching tattoos in July. The actress has several other tattoos, including the word "AppleHead -- a term of endearment for Michael Jackson -- which she got in June.
"With every step i take, you lift my foot and guide me forward. love you," she wrote on Instagram after getting the tattoo in her dad's honor.
Jackson attended the 2017 MTV Video Music Awards on Sunday, where she mocked President Donald Trump and denounced "white supremacist jerks" in a speech while presenting Best Pop Video to Fifth Harmony.