diff --git a/src/lib/style-transformer.html b/src/lib/style-transformer.html
index aa5a557222..fc493f9521 100644
--- a/src/lib/style-transformer.html
+++ b/src/lib/style-transformer.html
@@ -235,26 +235,21 @@
 
       // :host(...) -> scopeName...
       _transformHostSelector: function(selector, hostScope) {
-        var m = HOST_PAREN.exec(selector);
-        HOST_PAREN.lastIndex = 0;
-        var paren = m && m[2].trim();
-        if (paren) {
-          var selectorKind = /[[.:#*]/;
-          if (!paren[0].match(selectorKind)) {
-            var typeSelector = paren.split(selectorKind)[0];
-            if (typeSelector === hostScope) {
-              hostScope = '';
-            } else {
-              return SELECTOR_NO_MATCH;
-            }
+        var m = selector.match(HOST_PAREN);
+        var paren = m && m[2].trim() || '';
+        if (paren && !paren[0].match(SIMPLE_SELECTOR_PREFIX)) {
+          // paren starts with a type selector
+          var typeSelector = paren.split(SIMPLE_SELECTOR_PREFIX)[0];
+          // if the type selector is our hostScope then avoid pre-pending it
+          if (typeSelector === hostScope) {
+            return paren;
+          // otherwise, this selector should not match in this scope so
+          // output a bogus selector.
+          } else {
+            return SELECTOR_NO_MATCH;
           }
-          return selector.replace(HOST_PAREN, function(m, host, paren) {
-            return hostScope + paren;
-          });
-        } else {
-          // now normal :host
-          return selector.replace(HOST, hostScope);
         }
+        return hostScope + paren;
       },
 
       documentRule: function(rule) {
@@ -286,12 +281,13 @@
       ':not(.' + SCOPE_NAME + ')';
     var COMPLEX_SELECTOR_SEP = ',';
     var SIMPLE_SELECTOR_SEP = /(^|[\s>+~]+)((?:\[.+?\]|[^\s>+~=\[])+)/g;
+    var SIMPLE_SELECTOR_PREFIX = /[[.:#*]/;
     var HOST = ':host';
     var ROOT = ':root';
     // 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)(?:\(((?:\([^)(]*\)|[^)(]*)+?)\))/;
     var HOST_CONTEXT = ':host-context';
     var HOST_CONTEXT_PAREN = /(.*)(?::host-context)(?:\(((?:\([^)(]*\)|[^)(]*)+?)\))(.*)/;
     var CONTENT = '::content';