New players tend to make the same handful of mistakes. The rules behind them are simple; they are just easy to forget in the middle of a game. Here are ten common ones, each with the tiles that show it.
1. A joker in a pair
Jokers can be used to make three of a kind or more, but not pairs. A pair is always two real tiles.
Not allowed: a joker in a pair.
Allowed: a pair of two real 5 Dots, and three 8 Craks made with one joker.
2. A joker standing in for a single tile
The same rule covers single tiles. In the 2026 hand that spells the year, each of the four tiles is a single, so all four must be real.
Not allowed: a joker standing in for the second 2.
Allowed: 2, Soap, 2, 6, all real tiles. The Soap (the white dragon) stands for zero.
3. Passing a joker in the Charleston
Jokers may never be passed, not in the Charleston and not in the courtesy pass. If a joker sits among the tiles you don't want, keep it anyway: it is the most useful tile you have.
A good pass: three tiles your hand has no use for, and no joker among them.
4. Calling a thrown tile to make a pair
You may call a tile someone throws only to make three of a kind or more, unless that tile finishes your whole hand. Holding one 7 Dot and calling another for a pair is not allowed.
Allowed: calling the third 7 Dot to make three of a kind, which then goes face up on your rack.
5. Calling a tile for a hand marked C
A C at the end of a line on the card means concealed. You build that hand hidden on your rack and you may take a thrown tile for it only when that tile wins the game. Lines marked X can take called tiles.
6. Mixing suits when the card shows one colour
The card prints each line in colours. One colour means one suit: every number in that line comes from the same suit, any suit you choose. Two or three colours mean that many different suits.
Printed in one colour, so both groups are Bams. Four 2 Bams with four 4 Craks would not match.
7. Laying down a set that doesn't fit your hand
Once a set is face up it can't change, and the jokers in it stay in it. It can't grow later, and it can't lend a joker to another group. If your hand needs three Souths, show three, not four.
Three Souths, exactly what the hand needs.
8. Calling too late
A thrown tile can be called only until the next player draws from the wall. After that it stays in the middle for the rest of the game. Say "call" as soon as you see the tile you want.
9. Throwing a joker
Nobody may call a thrown joker, so once it leaves your rack it is gone for good. It can stand in for any tile in a group of three or more, which makes it almost always the most useful tile you hold.
One joker turns a pair of 4 Dots into three of a kind.
10. Trading for a joker before you draw
If a set face up on any rack has a joker in it, and you hold the real tile it stands for, you may trade your tile for the joker. Do it on your own turn, after you draw your tile: draw first, then trade.
Three 5 Bams face up with a joker. On your turn, after drawing, you can give the real 5 Bam and take the joker.
Questions
Can a joker be used in a pair in American Mah Jongg?
No. Jokers can be used to make three of a kind or more, but never a pair or a single tile. A pair is always two real tiles.
Can you pass a joker in the Charleston?
No. Jokers may never be passed, in any of the Charleston passes or in the courtesy pass.
Can you call a discard to make a pair?
Only when that tile finishes your whole hand and you declare Mah Jongg. Otherwise you may call a discard only to make three of a kind or more.
What does C mean on the mah jongg card?
Concealed. You build that hand hidden on your rack, and you may take a thrown tile for it only when that tile wins the game. X means you may call tiles for it.
Sources
The rules here follow the school's rules page: jokers, the Charleston, the turn and joker exchange. Each mistake is also in our video, 10 mistakes beginners make, on our YouTube channel.