diff --git a/dev-requirements.txt b/dev-requirements.txt
index 6a66f8d3..f66b3a27 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -16,6 +16,8 @@ pep517>=0.9.1
 # Safety CI by pyup.io
 safety>=2.2.0
 dparse>=0.6.2
+ruamel.yaml>=0.17.21,<0.17.22; python_version == '3.6'
+ruamel.yaml>=0.17.21; python_version >= '3.7'
 
 # Unit test (imports into testcases):
 # pytest 4.3.1 solves an issue on Python 3 with minimum package levels
diff --git a/minimum-constraints.txt b/minimum-constraints.txt
index 15b8e108..29be71d2 100644
--- a/minimum-constraints.txt
+++ b/minimum-constraints.txt
@@ -83,6 +83,7 @@ pep517==0.9.1
 # Safety is run only on Python >=3.6
 safety==2.2.0
 dparse==0.6.2
+ruamel.yaml==0.17.21
 
 # Unit test (imports into testcases):
 # pytest 4.3.1 solves an issue on Python 3 with minimum package levels