diff --git a/bin/post_version.py b/bin/post_version.py
index c4779f143d7..e2a3580e845 100755
--- a/bin/post_version.py
+++ b/bin/post_version.py
@@ -56,7 +56,7 @@ def update_calendar(version: str) -> None:
     p = pathlib.Path('docs') / 'release-calendar.csv'
 
     with p.open('r') as f:
-        calendar = csv.reader(f)
+        calendar = list(csv.reader(f))
 
     branch = None
     for i, line in enumerate(calendar):