diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index 2735bf8..a0b7569 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -39,6 +39,7 @@
     source ${VENV_DIR}/bin/activate
     python -m pip install "msgpack<1.0.0" "setuptools<45.0.0"
     python -m pip install salt${PIP_SALT_VERSION}
+    python -m pip install 'msgpack<1.0.0'
 }
 
 setup_pillar() {