diff --git a/certbot_dns_infomaniak/dns_infomaniak.py b/certbot_dns_infomaniak/dns_infomaniak.py
index fade23d..15296d7 100644
--- a/certbot_dns_infomaniak/dns_infomaniak.py
+++ b/certbot_dns_infomaniak/dns_infomaniak.py
@@ -213,7 +213,7 @@ def add_txt_record(self, domain, source, target, ttl=300):
         (domain_id, domain_name) = self._find_zone(domain)
         logger.debug("%s / %s", domain_id, domain_name)
         if source.endswith("." + domain_name):
-            relative_source = source[:source.rfind("." + domain_name)]
+            relative_source = source[:source.rfind("." + idna.encode(domain_name).decode("ascii"))]
         else:
             relative_source = source
         logger.debug("add_txt_record %s %s %s", domain_name, relative_source, target)
@@ -229,7 +229,7 @@ def del_txt_record(self, domain, source, target):
         logger.debug("del_txt_record %s %s %s", domain, source, target)
         (domain_id, domain_name) = self._find_zone(domain)
         if source.endswith("." + domain_name):
-            relative_source = source[:source.rfind("." + domain_name)]
+            relative_source = source[:source.rfind("." + idna.encode(domain_name).decode("ascii"))]
         else:
             relative_source = source
         records = self._get_records(