diff --git a/esphome/components/api/api.proto b/esphome/components/api/api.proto
index 271b1d6c5f..85706fcfcc 100644
--- a/esphome/components/api/api.proto
+++ b/esphome/components/api/api.proto
@@ -46,6 +46,7 @@ service APIConnection {
 // The Home Assistant protocol is structured as a simple
 // TCP socket with short binary messages encoded in the protocol buffers format
 // First, a message in this protocol has a specific format:
+//  * A zero byte.
 //  * VarInt denoting the size of the message object. (type is not part of this)
 //  * VarInt denoting the type of message.
 //  * The message object encoded as a ProtoBuf message