## 1. Data

We take TESS full-frame light curves for M dwarfs below 0.35 solar masses within 100 pc. Rotation periods come from a Lomb-Scargle periodogram with a false-alarm threshold of 0.1 per cent.

## 2. Saturation

Plotting activity against Rossby number, the relation is flat below a Rossby number of 0.12 and falls as a power law above it. We fit a broken power law with the break as a free parameter.

## 3. Discussion

The saturation point agrees with earlier estimates for partly convective stars, which suggests the dynamo changes little at the fully convective boundary.