diff --git a/requirements_dev.txt b/requirements_dev.txt
index 382179f..66538bf 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -12,4 +12,4 @@ pytest==6.2.5
 pytest-runner==5.3.1
 vcrpy==2.1.1
 twine==3.4.2
-black==21.8b0
+black==21.9b0