Larian Studios Forums Baldur's Gate III Baldur's Gate III - General "Dueling" passive with the shield

You get the dueling benefit with a shield in your other hand in early access, yes.

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Of note, at least in early access, you kind of have to have a shield in your other hand to get the bonus. Otherwise, the game assumes you're wielding a longsword, for example, as two handed instead of just one handed, giving you a d10 rather than a d8.