diff --git a/lib/esbonio-extensions/tox.ini b/lib/esbonio-extensions/tox.ini
index 9d662b4e4..7ad30657d 100644
--- a/lib/esbonio-extensions/tox.ini
+++ b/lib/esbonio-extensions/tox.ini
@@ -8,6 +8,7 @@ deps =
     build
     ../esbonio
     sphinx-design
+    myst-parser
 usedevelop = true
 allowlist_externals =
     cp