diff --git a/src/engine.ml b/src/engine.ml
index c909b49..58b7be0 100644
--- a/src/engine.ml
+++ b/src/engine.ml
@@ -574,7 +574,7 @@ let push_request tls =
 let push_reply tls data =
   (* a trailing 0 byte.. (String.make 1 '\000') *)
   let repl =
-    String.concat "" [ Packet.push_reply; data; String.make 1 '\000' ]
+    String.concat "" [ Packet.push_reply; data; "\000" ]
   in
   Option.to_result
     ~none:(`Msg "Tls.send application data failed for push request")