For more from Ginsburg, don’t miss Irin Carmon’s exclusive msnbc interview with the Supreme Court justice this Monday at 9 p.m. ET on “The Rachel Maddow Show.”

Supreme Court Justice Ruth Bader Ginsburg, who was seen nodding off last month during President Obama’s State of the Union address, offered a surprising explanation for her snooze.

I give Ruth Bader Ginsburg 5 minutes…pic.twitter.com/GQn9SeAN4H — Dave Briggs (@davebriggstv) January 21, 2015

“The audience for the most part is awake because they’re bobbing up and down all the time,” Ginsburg said, according to video of the event from CNN. “And we sit there, stone-faced, sober judges. But we’re not, at least I was not, 100% sober.”

Fellow Supreme Court Justices Stephen Breyer and Anthony Kennedy did their best to keep Ginsburg awake, delivering nearly a dozen subtle nudges and at least one elbow to keep the 81-year-old justice alert — or at least prevent her from slumping over. But in the end, the president’s hour-long speech got the upper hand.

Most of the Supreme Court justices gather for dinner each year before the annual State of the Union speech, Ginsburg explained, and Justice Kennedy had brought “a very fine California wine” that she couldn’t turn down — despite her history of wine-fueled naps.

“I vowed this year — just sparkling water, stay away from the wine,” said Ginsburg, who also fell asleep during the State of the Union in 2010 and 2013. “But in the end the dinner was so delicious it needed wine to accompany it.”

The Supreme Court justice got an earful from one of her granddaughters when she got home: “She said, ‘Bubbe! You were sleeping at the State of the Union!’”