"HBDJ," he wrote next to a super-cute -- and rare -- selfie of the couple on Instagram, with Jen blowing a kiss to the camera.
"The Leftovers" star even added a heart emoji in his caption, and ended it with a "XO."
Jennifer, who turned 48 years old, married Justin, 45, quietly in 2015.
The pair hardly ever shares personal photos on social media, so the pic came as a bit of a surprise.
His last photo of his wife was posted almost exactly one year ago, featuring Jen peering out at the Eiffel Tower in Paris.
According to Us Weekly, the couple is currently vacationing in Cabo San Lucas, Mexico to celebrate.
And, they're apparently spending their down time with Jennifer's old "Friends" co-star Courteney Cox and her man Johnny McDaid.
Happy birthday, Jen!