diff --git a/requirements.txt b/requirements.txt
index b93a3e3..ad6b942 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,7 @@ aiounittest
 async_generator
 juju
 juju_wait
-PyYAML
+PyYAML<=4.2,>=3.0 
 flake8>=2.2.4,<=3.5.0
 flake8-docstrings
 flake8-per-file-ignores