diff --git a/setup.cfg b/setup.cfg
index 45ab855..9b43c99 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -50,6 +50,7 @@ dev =
     ufmt == 2.3.0
     usort == 1.0.7
     wheel == 0.42.0
+    pessimist >= 0.9.4b1, < 1.0
 test =
     coverage >= 6
     setuptools >= 65 ; python_version >= '3.12'