diff --git a/pyproject.toml b/pyproject.toml
index 07f1871..35de646 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,7 +17,7 @@ dependencies = [
     "numpy",
     "opencv-python",
     "pyboy>=2",
-    "pufferlib[cleanrl]>=0.7.3",
+    "pufferlib[cleanrl]>=0.7.3,<1.0.0",
     "scikit-image",
     "torch>=2.1",
     "torchvision",