diff --git a/tox.ini b/tox.ini
index ce1dc65..76ba5a3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,6 +14,7 @@ isolated_build = true
 [testenv]
 depends = test: clean
 docker = test: postgres
+constrain_package_deps = true
 deps =
     test: pytest
     test: pytest-cov