diff --git a/phamlp/sass/script/SassScriptParser.php b/phamlp/sass/script/SassScriptParser.php
index 39bb4fa..41958ae 100644
--- a/phamlp/sass/script/SassScriptParser.php
+++ b/phamlp/sass/script/SassScriptParser.php
@@ -123,8 +123,8 @@ class SassScriptParser {
 		foreach($tokens as $i=>$token) {
 			// If two literals/expessions are seperated by whitespace use the concat operator
 			if (empty($token)) {
-				if ($i > 0 && (!$tokens[$i-1] instanceof SassScriptOperation || $tokens[$i-1]->operator === SassScriptOperation::$operators[')'][0]) &&
-						(!$tokens[$i+1] instanceof SassScriptOperation || $tokens[$i+1]->operator === SassScriptOperation::$operators['('][0])) {
+				if ($i > 0 && (isset($tokens[$i-1]) && !$tokens[$i-1] instanceof SassScriptOperation || isset($tokens[$i-1]) && $tokens[$i-1]->operator === SassScriptOperation::$operators[')'][0]) &&
+						(isset($tokens[$i+1]) && !$tokens[$i+1] instanceof SassScriptOperation || isset($tokens[$i+1]) && $tokens[$i+1]->operator === SassScriptOperation::$operators['('][0])) {
 					$token = new SassScriptOperation(SassScriptOperation::$defaultOperator, $context);
 				}
 				else {