diff --git a/pyproject.toml b/pyproject.toml
index ab6724a..a2c3779 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,7 @@ Repository = "https://github.com/RascalSoftware/python-RAT"
 
 [project.optional-dependencies]
 dev = [
-    "pytest>=7.4.0",
+    "pytest>=7.4.0,!=9.1.0",
     "pytest-cov>=4.1.0",
     "ruff>=0.4.10"
 ]