diff --git a/lib/less/parser.js b/lib/less/parser.js
index 4939a9b..2e6fffb 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -238,7 +238,7 @@ less.parser = {
                 var number, unit;
 
                 number = $(/-?[0-9]*\.?[0-9]+/g);
-                unit = $(/(?:px|%|em|pc|ex|in|deg|s|pt|cm|mm)/g);
+                unit = $(/(?:px|%|em|pc|ex|in|deg|s|ms|pt|cm|mm)/g);
 
                 if (number) { return new(node.Dimension)(number, unit) }
             }