diff --git a/README.md b/README.md
index 233f61c..4733e07 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,8 @@ bumped if the envelope format changes or if the message encoding changes in a
 non-backwards-compatible way. Adding fields to the messages should not require
 a version bump.
 
+Currently, the only supported protocol version is v0, i.e. `0x00`.
+
 #### HeaderLen [1 byte]
 
 The header length is the offset of the payload. This is included primarily for