diff --git a/helpers/postgresql.py b/helpers/postgresql.py
index d682bd4e..7e4d4c22 100644
--- a/helpers/postgresql.py
+++ b/helpers/postgresql.py
@@ -126,7 +126,7 @@ class Postgresql:
                 member_conn = psycopg2.connect(member["address"])
                 member_conn.autocommit = True
                 member_cursor = member_conn.cursor()
-                member_cursor.execute("SELECT '%s'::pg_lsn - pg_last_xlog_replay_location() AS bytes;" % self.xlog_position())
+                member_cursor.execute("SELECT %s - (pg_last_xlog_replay_location() - '0/000000'::pg_lsn) AS bytes;" % self.xlog_position())
                 xlog_diff = member_cursor.fetchone()[0]
                 logger.info([self.name, member["hostname"], xlog_diff])
                 if xlog_diff < 0:
@@ -181,4 +181,4 @@ recovery_target_timeline = 'latest'
         self.query("CREATE USER \"%s\" WITH REPLICATION ENCRYPTED PASSWORD '%s';" % (self.replication["username"], self.replication["password"]))
 
     def xlog_position(self):
-        return self.query("SELECT pg_last_xlog_replay_location();").fetchone()[0]
+        return self.query("SELECT pg_last_xlog_replay_location() - '0/0000000'::pg_lsn;").fetchone()[0]