diff --git a/.travis.yml b/.travis.yml
index a771c372d..4f17e7fd8 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,6 +14,7 @@ env:
   matrix:
     - TOXENV=py26 BOULDER_INTEGRATION=1
     - TOXENV=py27 BOULDER_INTEGRATION=1
+    - TOXENV=py33
     - TOXENV=py34
     - TOXENV=lint
     - TOXENV=cover
diff --git a/tox.ini b/tox.ini
index a2d4fbde7..1921fdd9c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,7 +6,7 @@
 # acme and letsencrypt are not yet on pypi, so when Tox invokes
 # "install *.zip", it will not find deps
 skipsdist = true
-envlist = py26,py27,py34,cover,lint
+envlist = py26,py27,py33,py34,cover,lint
 
 [testenv]
 commands =
@@ -22,6 +22,11 @@ setenv =
     PYTHONHASHSEED = 0
 # https://testrun.org/tox/latest/example/basic.html#special-handling-of-pythonhas
 
+[testenv:py33]
+commands =
+    pip install -e acme[testing]
+    nosetests acme
+
 [testenv:py34]
 commands =
     pip install -e acme[testing]