What if you expose the wrong tiles with a called discard?
By Jerry Chen. Checked and updated November 1, 2026
Short answer: fix it before you discard
You can fix it before you discard. If you exposed more than one group at once by mistake, though, the hand is dead.
The detail
For example, you call a 5 bam but put up two 5 craks beside it. The League's January 2025 bulletin lets you change the number and type of tiles in that exposure until you have discarded.
After your discard the exposure is locked, and if it fits no hand, the hand can be called dead.
Sources
These follow standard National Mah Jongg League rules. House rules vary; agree on them before you play.
Related questions
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See more questions in Calling discards and exposures, the complete rules, or all 52 rule questions.