diff --git a/tox.ini b/tox.ini
index a1ae8444..a7921c61 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = {py27,py35,pypy,pypy3}-{mg34,mg36}
+envlist = {py27,py35,pypy,pypy3}-{mg34,mg36, mg39}
 
 [testenv]
 commands =
@@ -8,5 +8,6 @@ deps =
     nose
     mg34: pymongo>=3.4,<3.5
     mg36: pymongo>=3.6,<3.7
+    mg39: pymongo>=3.9,<4.0
 setenv =
     PYTHON_EGG_CACHE = {envdir}/python-eggs