diff --git a/lessc.inc.php b/lessc.inc.php
index a44b3f58..73b4dda7 100644
--- a/lessc.inc.php
+++ b/lessc.inc.php
@@ -662,7 +662,7 @@ protected function zipSetArgs($args, $orderedValues, $keywordValues) {
 
 		// check for a rest
 		$last = end($args);
-		if ($last[0] == "rest") {
+		if (is_array($last) && isset($last[0]) && $last[0] == "rest") {
 			$rest = array_slice($orderedValues, count($args) - 1);
 			$this->set($last[1], $this->reduce(array("list", " ", $rest)));
 		}