diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7cd7228..d6e51d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+(unreleased)
+------------------
+
 5.2.1 / 2025/04/28
 ------------------
 * セキュリティに関する修正