diff --git a/.changeset/tidy-starfishes-bathe.md b/.changeset/tidy-starfishes-bathe.md
new file mode 100644
index 0000000..55660c2
--- /dev/null
+++ b/.changeset/tidy-starfishes-bathe.md
@@ -0,0 +1,5 @@
+---
+"windpipe": patch
+---
+
+Fix json serialisation issue when stream contains undefined values