diff --git a/README.md b/README.md
index 1a37a8e5..39b09c0f 100644
--- a/README.md
+++ b/README.md
@@ -479,6 +479,10 @@ with the UUID of the session.
 In case of attempt to use an invalid format UUID or expired UUID, an error will
 be thrown.
 
+Be careful, UUID here is a 16-bit string generated by
+[uuid.bin()](https://www.tarantool.io/en/doc/latest/reference/reference_lua/uuid/#lua-function.uuid.bin),
+not an object of type UUID.
+
 Usage example:  
 Sometimes we need an ability to acknowledge a task after reconnect (because
 retrying it is undesirable) or even acknowlegde using another connection.