diff --git a/doc/install.rst b/doc/install.rst
index 3eee2d20..abdc7bc1 100644
--- a/doc/install.rst
+++ b/doc/install.rst
@@ -9,7 +9,7 @@ Installation
 Prerequisites
 -------------
 
-#. Python3
+#. Python3 (>=3.8)
 
 #. You will also need at least one impurity solver.
 
diff --git a/setup.py b/setup.py
index 1ac31f5d..64068578 100644
--- a/setup.py
+++ b/setup.py
@@ -39,9 +39,9 @@
         ]),
     author_email='h.shinaoka@gmail.com',
 
-    python_requires='>=3.6, <4',
+    python_requires='>=3.8, <4',
     install_requires=[
-        'numpy',
+        'numpy<2',
         'scipy>=1.4',
         # h5py 2.10.0 has a bug.
         # Import h5py imports mpi4py automatically.