diff --git a/src/config.hpp b/src/config.hpp
index bde83600..e9217c48 100644
--- a/src/config.hpp
+++ b/src/config.hpp
@@ -59,12 +59,6 @@ namespace zmq
         //  unnecessary network stack traversals.
         in_batch_size = 8192,
 
-        //  Maximal batching size for engines with sending functionality.
-        //  So, if there are 10 messages that fit into the batch size, all of
-        //  them may be written by a single 'send' system call, thus avoiding
-        //  unnecessary network stack traversals.
-        out_batch_size = 8192,
-
         //  Maximal delta between high and low watermark.
         max_wm_delta = 1024,