diff --git a/dev-requirements.txt b/dev-requirements.txt
index 04a0b319..055ba585 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -37,6 +37,8 @@ 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:
 # 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 ce6c4db1..96cd6397 100644
--- a/minimum-constraints.txt
+++ b/minimum-constraints.txt
@@ -102,6 +102,7 @@ pep517==0.9.1
 # Safety CI by pyup.io
 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