diff --git a/.changeset/giant-plums-grin.md b/.changeset/giant-plums-grin.md
new file mode 100644
index 00000000..f920e52f
--- /dev/null
+++ b/.changeset/giant-plums-grin.md
@@ -0,0 +1,6 @@
+---
+"@otterhttp/cookie": patch
+"@otterhttp/response": patch
+---
+
+Fix: don't allow an `undefined` value to override a non-nullish value in `SetCookieOptions`