diff --git a/setup.cfg b/setup.cfg
index 6a731e67..0cf1da70 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -38,7 +38,8 @@ classifiers =
 include_package_data = True
 install_requires=
     async_generator
-    attrs
+    # >= 20.1.0 for attr.frozen
+    attrs >= 20.1.0
     decorator
     outcome
     qts ~= 0.2.0