identify_system_msg.diff

diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 60d5c1fc40..b402379d12 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -381,6 +381,10 @@ libpqrcv_identify_system(WalReceiverConn *conn, TimeLineID *primary_tli)
 						"the primary server: %s",
 						pchomp(PQerrorMessage(conn->streamConn)))));
 	}
+	/*
+	 * IDENTIFY_SERVER returns 3 columns in 9.3 and earlier, and 4 columns in
+	 * 9.4 and onwards.
+	 */
 	if (PQnfields(res) < 3 || PQntuples(res) != 1)
 	{
 		int			ntuples = PQntuples(res);
@@ -391,7 +395,7 @@ libpqrcv_identify_system(WalReceiverConn *conn, TimeLineID *primary_tli)
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
 				 errmsg("invalid response from primary server"),
 				 errdetail("Could not identify system: got %d rows and %d fields, expected %d rows and %d or more fields.",
-						   ntuples, nfields, 3, 1)));
+						   ntuples, nfields, 1, 4)));
 	}
 	primary_sysid = pstrdup(PQgetvalue(res, 0, 0));
 	*primary_tli = pg_strtoint32(PQgetvalue(res, 0, 1));