diff --git a/lib/transformer.js b/lib/transformer.js
index 99bbae8..2326c95 100644
--- a/lib/transformer.js
+++ b/lib/transformer.js
@@ -58,7 +58,8 @@ function getAttributeIndex (tag, attr) {
 }
 
 function createClassPrefix(classPrefix) {
-    var re = /\.[\w\-]+/g;
+    //http://stackoverflow.com/questions/12391760/regex-match-css-class-name-from-single-string-containing-multiple-classes
+    var re = /\.(-?[_a-zA-Z]+[_a-zA-Z0-9-]*)(?![^\{]*\})/g;
     var inStyleTag = false;
 
     return function prefixClasses(tag) {