*** a/src/backend/replication/walsender.c
--- b/src/backend/replication/walsender.c
***************
*** 263,268 **** WalSndHandshake(void)
--- 263,269 ----
  						pq_sendbyte(&buf, 0);
  						pq_sendint(&buf, 0, 2);
  						pq_endmessage(&buf);
+ 						pq_flush();
  
  						/*
  						 * Initialize position to the received one, then the