diff --git a/ChangeLog.d/chacha20_invalid_iv_len_fix.txt b/ChangeLog.d/chacha20_invalid_iv_len_fix.txt
new file mode 100644
index 000000000..af35e2a00
--- /dev/null
+++ b/ChangeLog.d/chacha20_invalid_iv_len_fix.txt
@@ -0,0 +1,4 @@
+Default behavior changes
+   * mbedtls_cipher_set_iv will now fail with ChaCha20 and ChaCha20+Poly1305
+     for IV lengths other than 12. The library was silently overwriting this
+     length with 12, but did not inform the caller about it. Fixes #4301.