04/04/2011 at 09:45 AM EDT
celebrated his mom's birthday on stage Saturday night – with some unexpected pyrotechnics.
The pop star, 17, surprised Pattie Mallette with a birthday cake at the end of the concert at Berlin's O2 World arena. But as she leaned over the cake to blow out the candles, a few strands of her hair caught on fire.
Bieber quickly put out the flames, and then said, "Mama, I'll always be your baby," according to Germany's Bild
Mother and son both Tweeted about the incident later. Bieber wrote
: "sick show in Berlin...brought @studiomama on stage 2 sing her happy bday but she lit her hair on fire with the candles. lol. i saved her."
: "Thank u @justinbieber for the cake (& embarrassing me on stage lol)."