diff --git a/‎src/lib/style-transformer.html‎
Lines changed: 26 additions & 6 deletions b/‎src/lib/style-transformer.html‎
Lines changed: 26 additions & 6 deletions
diff --git a/‎test/unit/styling-scoped-elements.html‎
Lines changed: 4 additions & 0 deletions b/‎test/unit/styling-scoped-elements.html‎
Lines changed: 4 additions & 0 deletions
diff --git a/‎test/unit/styling-scoped.html‎
Lines changed: 8 additions & 0 deletions b/‎test/unit/styling-scoped.html‎
Lines changed: 8 additions & 0 deletions
@@ -206,12 +206,7 @@
         if (selector.indexOf(HOST_CONTEXT) >=0) {
           hostContext = true;
         } else if (selector.indexOf(HOST) >=0) {
-          // :host(...) -> scopeName...
-          selector = selector.replace(HOST_PAREN, function(m, host, paren) {
-            return (m.indexOf(hostScope) === -1 ? hostScope : '') + paren;
-          });
-          // now normal :host
-          selector = selector.replace(HOST, hostScope);
+          selector = this._transformHostSelector(selector, hostScope);
         // replace other selectors with scoping class
         } else if (jumpIndex !== 0) {
           selector = scope ? this._transformSimpleSelector(selector, scope) :
@@ -238,6 +233,30 @@
         return p$.join(PSEUDO_PREFIX);
       },
 
+      // :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;
+            }
+          }
+          return selector.replace(HOST_PAREN, function(m, host, paren) {
+            return hostScope + paren;
+          });
+        } else {
+          // now normal :host
+          return selector.replace(HOST, hostScope);
+        }
+      },
+
       documentRule: function(rule) {
         // reset selector in case this is redone.
         rule.selector = rule.parsedSelector;
@@ -283,6 +302,7 @@
     var PSEUDO_PREFIX = ':';
     var CLASS = 'class';
     var CONTENT_START = new RegExp('^(' + CONTENT + ')');
+    var SELECTOR_NO_MATCH = 'should_not_match';
 
     // exports
     return api;
 
@@ -554,6 +554,10 @@
         display: block;
         border: 4px solid orange;
       }
+
+      :host(.x-shared1) {
+        padding: 8px;
+      };
     </style>
   </template>
 </dom-module>
 
@@ -410,6 +410,14 @@
       assertComputed(s2, '4px');
     });
 
+    test(':host with superset of element tag selector does not leak', function() {
+      var t = document.createElement('div');
+      t.textContent = 'host leak test';
+      t.classList.add('x-shared1');
+      document.body.appendChild(t);
+      assertComputed(t, '0px', 'padding');
+    });
+
 });
 
 </script>