diff --git a/check_syncrepl_extended b/check_syncrepl_extended
index 70525ec..e92069f 100755
--- a/check_syncrepl_extended
+++ b/check_syncrepl_extended
@@ -323,7 +323,7 @@ class LdapServer(object):
             if serverid is False:
                 return contextCSNs[0]
             csnid = str(format(serverid, 'X')).zfill(3)
-            sub = '#%s#' % csnid
+            sub = str.encode('#%s#' % csnid, encoding="ascii", errors="replace")
             CSN = [s for s in contextCSNs if sub in s]
             if not CSN:
                 logging.error(