yǐ​fáng​wàn​yī

just in case

以防万一 以防萬一 yǐ​fáng​wàn​yī
just in case adverb
(idiom) to guard against the unexpected; to be prepared for any eventuality or emergency

“Oh, just in case, here’s my name and address,” he said, handing her a card.

Frequency

Movie subtitles
12.4 per million appears in 6% of films
Written text
0.714 per million

Sources