diff --git a/tox.ini b/tox.ini
index 48d9ab3..59bd5e5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -48,6 +48,7 @@ commands        = mypy -p setools
 passenv         = USERSPACE_SRC
 deps            = networkx>=2.0
                   cython>=0.27
+                  py36: dataclasses
                   py38: cython>=0.29.14
                   py39: networkx>=2.6
                   py39: cython>=0.29.14