diff --git a/CHANGELOG b/CHANGELOG
index d6bf90f2c..fc996d1e5 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -74,6 +74,7 @@ CHANGELOG Roundcube Webmail
 - Fix touch event issue on messages list in IE/Edge (#5781)
 - Fix so links over images are not removed in plain text signatures converted from HTML (#4473)
 - Fix various issues when downloading files with names containing non-ascii chars, use RFC 2231 (#5772)
+- Fix PHP Warning: Use of undefined constant IDNA_DEFAULT on systems without php-intl (#6244)
 
 RELEASE 1.3.6
 -------------
diff --git a/program/lib/Roundcube/rcube_utils.php b/program/lib/Roundcube/rcube_utils.php
index 7dbc051f9..5fcb4476e 100644
--- a/program/lib/Roundcube/rcube_utils.php
+++ b/program/lib/Roundcube/rcube_utils.php
@@ -959,7 +959,7 @@ class rcube_utils
         // Note that in PHP 7.2/7.3 calling idn_to_* functions with default arguments
         // throws a warning, so we have to set the variant explicitely (#6075)
         $variant = defined('INTL_IDNA_VARIANT_UTS46') ? INTL_IDNA_VARIANT_UTS46 : null;
-        $options = IDNA_DEFAULT;
+        $options = 0;
 
         // Because php-intl extension lowercases domains and return false
         // on invalid input (#6224), we skip conversion when not needed