diff --git a/constraints-oldest.txt b/constraints-oldest.txt
index b639e274e..19b465fd7 100644
--- a/constraints-oldest.txt
+++ b/constraints-oldest.txt
@@ -5,6 +5,7 @@
 # versions in `setup.cfg`.
 airium==0.2.3
 black==21.8b0
+blue==0.8.0
 defusedxml==0.7.1
 flake8-2020==1.6.1
 flake8-bugbear==22.1.11
diff --git a/setup.cfg b/setup.cfg
index c08f7122c..9228faac1 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -49,6 +49,8 @@ isort =
     isort>=5.0.1
 color =
     Pygments>=2.4.0
+blue =
+    blue>=0.8.0
 test =
     # NOTE: remember to keep `constraints-oldest.txt` in sync with these
     airium>=0.2.3