diff --git a/pyproject.toml b/pyproject.toml
index 75e8b970..7740ce0c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,7 @@ requires-python = '>=3.7'
 dependencies = [
     'psutil',
     'pyzmq>=17.0',
-    'tornado>=5.0.2',
+    'tornado>=5.0.2,<6.0',
 ]
 
 [project.urls]