diff --git a/requirements.txt b/requirements.txt
index 202477b..bf262f0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,7 +13,8 @@ importlib-metadata==0.17
 Jinja2==2.10.1
 MarkupSafe==1.1.1
 more-itertools==7.0.0
-numpy==1.21.3
+numpy==1.16.4; python_version < '3.9'
+numpy==1.21.3; python_version >= '3.9'
 packaging==19.0
 pluggy==0.12.0
 py==1.8.0