diff --git a/resources/classes/button.php b/resources/classes/button.php
index 8af56f1f05..c10ee3c017 100644
--- a/resources/classes/button.php
+++ b/resources/classes/button.php
@@ -59,7 +59,9 @@ if (!class_exists('button')) {
 				$button .= $array['onclick'] ? "onclick=".self::quote($array['onclick'])." " : null;
 				$button .= $array['onmouseover'] ? "onmouseenter=".self::quote($array['onmouseover'])." " : null;
  				$button .= $array['onmouseout'] ? "onmouseleave=".self::quote($array['onmouseout'])." " : null;
-				$button .= "class='btn btn-".($array['class'] ? $array['class'] : 'default')." ".($array['disabled'] ? 'disabled' : null)."' ";
+				//detect class addition (using + prefix)
+				$button_class = $array['class'] && $array['class'][0] == '+' ? 'default '.substr($array['class'], 1) : $array['class'];
+				$button .= "class='btn btn-".($button_class ? $button_class : 'default')." ".($array['disabled'] ? 'disabled' : null)."' ";
 				//ensure margin* styles are not applied to the button element when a link is defined
 				if (is_array($array['style']) && @sizeof($array['style']) != 0) {
 					foreach ($array['style'] as $property => $value) {