diff --git a/setup.py b/setup.py
index 6bed5b573..f27f3b3e3 100644
--- a/setup.py
+++ b/setup.py
@@ -31,7 +31,8 @@
     "autoapi",
     "ipython",
     "rstcheck",
-    "sphinx",
+    "pydantic<2",  # remove this when ert unpins fastapi and pydantic
+    "sphinx<7",
     "sphinx-argparse",
     "sphinx-autodoc-typehints",
     "sphinx_rtd_theme",