diff --git a/docker/tox.ini b/docker/tox.ini
index 5a5d24e..1405e8f 100644
--- a/docker/tox.ini
+++ b/docker/tox.ini
@@ -1,30 +1,31 @@
 [tox]
 envlist=flake8,py3,shell_tests
 
 [testenv]
 skip_install = true
 passenv = COMPOSE_FILE
 deps =
   pytest
   testinfra
   docker-compose
+  pdbpp
 commands =
   ## this 'build' step is disabled for now because it fails with a somewhat
   ## cryptic traceback about the secretservice library. So it must be managed
   ## by hand from outside the tox invocation.
   # docker-compose build swh-storage
   pytest {posargs}
 
 [testenv:flake8]
 deps =
   flake8
 commands =
   {envpython} -m flake8 tests
 
 [testenv:shell_tests]
 deps =
   docker-compose
 whitelist_externals =
   /bin/bash
 commands =
   /bin/bash tests/run_tests.sh