diff --git a/setup.py b/setup.py
index 4b9d6914fc..5d24e1f908 100644
--- a/setup.py
+++ b/setup.py
@@ -91,7 +91,7 @@
         # for parameter_sweep
         "h5py",
         # for watertap.ui.api_model (though may be generally useful)
-        "pydantic",
+        "pydantic < 2",
         "numpy",
         # for importlib.metadata.entry_points()
         "importlib_metadata; python_version < '3.8' ",