diff --git a/css/TreeDropdownField.css b/css/TreeDropdownField.css
index 026d1e4c3..a1ab36876 100644
--- a/css/TreeDropdownField.css
+++ b/css/TreeDropdownField.css
@@ -52,6 +52,7 @@ div.TreeDropdownField div.tree_holder iframe {
 	display:none;/* IE5*/
 	display/**/:block;/* IE5*/
 	position:absolute;
+	border-style: none;
 	top:0;
 	left:0;
 	z-index:-1;