diff --git a/htdocs/core/lib/ajax.lib.php b/htdocs/core/lib/ajax.lib.php
index 2ddc7125d4a..856d7cdfbd1 100644
--- a/htdocs/core/lib/ajax.lib.php
+++ b/htdocs/core/lib/ajax.lib.php
@@ -425,7 +425,8 @@ function ajax_combobox($htmlname, $events=array(), $minLengthToAutocomplete=0, $
 					},
 					escapeMarkup: function(markup) {
 						return markup;
-					}
+					},
+					dropdownCssClass: \'ui-dialog\'
 				})';
 	if ($forcefocus) $msg.= '.select2(\'focus\')';
 	$msg.= ';'."\n";