diff --git a/README.md b/README.md
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--- a/README.md
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 # nbformat: Jupyter Notebook Format
 
-[![codecov.io](https://codecov.io/github/jupyter/nbformat/coverage.svg?branch=master)](https://codecov.io/github/jupyter/nbformat?branch=master)
+[![codecov.io](https://codecov.io/github/jupyter/nbformat/coverage.svg?branch=main)](https://codecov.io/github/jupyter/nbformat/coverage.svg?branch=main)
 ![CI Tests](https://github.com/jupyter/nbformat/workflows/Run%20tests/badge.svg)
 
 `nbformat` contains the reference implementation of the [Jupyter Notebook format],