diff --git a/setup.py b/setup.py
index 8ba28845fe..33ecfcb6b8 100644
--- a/setup.py
+++ b/setup.py
@@ -55,7 +55,7 @@
         'gym==0.25.1',  # pypy incompatible; some environments only support gym==0.22.0
         'gymnasium',
         'torch>=1.1.0',
-        'numpy>=1.18.0',
+        'numpy>=1.18.0,<2',
         'DI-treetensor>=0.4.0',
         'DI-toolkit>=0.1.0',
         'trueskill',