diff --git a/setup.py b/setup.py
index 6bed5b573..600c90de3 100644
--- a/setup.py
+++ b/setup.py
@@ -23,6 +23,7 @@
     "pyarrow",
     "pyyaml>=5.1",
     "treelib",
+    "pydantic<2",
 ]
 
 TEST_REQUIREMENTS = Path("test_requirements.txt").read_text().splitlines()