diff --git a/requirements.txt b/requirements.txt
index 21c3801..ff21bc5 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-setuptools!=24.0.0,!=34.0.0,!=34.0.1,!=34.0.2,!=34.0.3,!=34.1.0,!=34.1.1,!=34.2.0,!=34.3.0,!=34.3.1,!=34.3.2,!=36.2.0,>=16.0 # PSF/ZPL
+setuptools!=24.0.0,!=34.0.0,!=34.0.1,!=34.0.2,!=34.0.3,!=34.1.0,!=34.1.1,!=34.2.0,!=34.3.0,!=34.3.1,!=34.3.2,!=36.2.0,>=21.0.0 # PSF/ZPL
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 keystoneauth1>=3.4.0 # Apache-2.0
 cliff!=2.9.0,>=2.8.0 # Apache-2.0