diff --git a/tox.ini b/tox.ini
index fc44eec061..59aacaab9c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,7 +14,7 @@ setenv =
   PYTHONDONTWRITEBYTECODE = 1
   # TODO(amotoki): There are three variants of PYTHONWARNINGS. They should be merged.
   PYTHONWARNINGS = once,ignore::PendingDeprecationWarning
-  py{3,39}:PYTHONWARNINGS = once,ignore::PendingDeprecationWarning,ignore::ImportWarning:backports
+  py{3,39}: PYTHONWARNINGS = once,ignore::PendingDeprecationWarning,ignore::ImportWarning:backports
   # DeprecationWarning is disabled in dj32 tox env as Django 3.2
   # deprecated Django 2.2 features. This workaround is just to reduce
   # the number of warnings due to this change.