diff --git a/pyproject.toml b/pyproject.toml
index a50f8a43..54517d0a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -51,7 +51,7 @@ classifiers = [
 
 [project.optional-dependencies]
 test = ["pytest >= 3.8", "hypothesis >= 6.28.0"]
-pydantic = ["pydantic>=1.8.2"]
+pydantic = ["pydantic>=1.8.2,<2.0.0"]
 beartype = ["beartype>=0.8.0"]
 
 [project.urls]