diff --git a/htdocs/core/class/extrafields.class.php b/htdocs/core/class/extrafields.class.php
index 99ec23c6a73beabb96ca19542de3c3b8a9179f2b..40ba0e666ae6191c0397efea072e2526cee6162d 100644
--- a/htdocs/core/class/extrafields.class.php
+++ b/htdocs/core/class/extrafields.class.php
@@ -1155,7 +1155,7 @@ class ExtraFields
 				else if (in_array($key_type,array('checkbox')))
 				{
 					$value_arr=GETPOST("options_".$key.$keyprefix);
-					$value_key=implode($value_arr,',');
+					$value_key=implode(',', $value_arr);
 				}
 				else if (in_array($key_type,array('price','double')))
 				{