diff --git a/tox.ini b/tox.ini
index 5bdc898..544b34a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -42,6 +42,7 @@ commands =
     python3 -m pip install --upgrade pip>=9.0.0 setuptools wheel
     pip3 install \
         pytest>=5.4.2 \
+        pyyaml==5.4.1 \
         simplejson \
         mock \
         rtyaml \