diff --git a/pyproject.toml b/pyproject.toml
index 761bcfc..6eff4b0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -44,7 +44,7 @@ invoke = "^2.2.0"
 hypothesis = "^6.108"
 tomli = "^2.2.1"
 black = ">=24.1,<26.0"
-isort = "^5.13.2"
+isort = ">=5.13.2,<8.0.0"
 flake8 = "^6.1.0"
 scikit-survival = "^0.24.1"
 pre-commit = "^3.8"