diff --git a/tox.ini b/tox.ini
index d6f96e2..446c58d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -15,6 +15,7 @@ commands=
     backends: py.test {posargs:tests/backends}
 deps = .[test]
     backends: coincurve>=7.0.0,<8.0.0
+              asn1tools>=0.146.1,<1.0.0
 setenv =
     backends: REQUIRE_COINCURVE=True
 basepython =