diff --git a/tox.ini b/tox.ini
index b1061a57c6a136cb29f77a1d0c03383ab82ecf8b..ed6cb25ed04267d54bd6971f8a485ec10138ebe3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,5 +7,6 @@ deps = .
     nose
     pytest
     pytest-cov
+    python-dateutil
     jsonschema==4.0.1
 commands=py.test --cov=caosdb -vv {posargs}