diff --git a/pyproject.toml b/pyproject.toml
index 2d43a9a98..01ee709f9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -45,7 +45,7 @@ dependencies = [
   "pymongo",
   "loguru",
   "lightgbm",
-  "gymnasium",
+  "gymnasium<=0.26.2",
   "cvxpy",
   "joblib",
   "matplotlib",