diff --git a/src/lib/style-transformer.html b/src/lib/style-transformer.html
index a8832f7a..419c38d6 100644
--- a/src/lib/style-transformer.html
+++ b/src/lib/style-transformer.html
@@ -159,7 +159,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         var stop = false;
         var hostContext = false;
         var self = this;
-        selector = selector.replace(/^(::content)/, ':host $1');
+        selector = selector.replace(CONTENT_START, HOST + ' $1');
         selector = selector.replace(SIMPLE_SELECTOR_SEP, function(m, c, s) {
           if (!stop) {
             var info = self._transformCompoundSelector(s, c, scope, hostScope);
@@ -255,7 +255,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     // NOTE: this supports 1 nested () pair for things like
     // :host(:not([selected]), more general support requires
     // parsing which seems like overkill
-    var HOST_PAREN = /(\:host)(?:\(((?:\([^)(]*\)|[^)(]*)+?)\))/g;
+    var HOST_PAREN = /(:host)(?:\(((?:\([^)(]*\)|[^)(]*)+?)\))/g;
     var HOST_CONTEXT = ':host-context';
     var HOST_CONTEXT_PAREN = /(.*)(?::host-context)(?:\(((?:\([^)(]*\)|[^)(]*)+?)\))(.*)/;
     var CONTENT = '::content';
@@ -265,6 +265,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     var CSS_ATTR_SUFFIX = ']';
     var PSEUDO_PREFIX = ':';
     var CLASS = 'class';
+    var CONTENT_START = new RegExp('^(' + CONTENT + ')');
 
     // exports
     return api;