diff --git a/requirements.txt b/requirements.txt
index 307fa94..1ee936a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,6 +7,7 @@ PyYAML<=4.2,>=3.0
 flake8>=2.2.4,<=3.5.0
 flake8-docstrings
 flake8-per-file-ignores
+pydocstyle<4.0.0
 coverage
 mock>=1.2
 nose>=1.3.7
@@ -36,4 +37,4 @@ paramiko
 # Documentation requirements
 sphinx
 sphinxcontrib-asyncio
-git+https://github.com/openstack-charmers/zaza#egg=zaza
\ No newline at end of file
+git+https://github.com/openstack-charmers/zaza#egg=zaza