diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index fcfeafc96e2..9ceaa5bfb8e 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -32931,7 +32931,18 @@ void _registerCustomElement(context, document, String tag, Type type,
   if (baseClassName == null) {
     throw new ArgumentError(type);
   }
-  if (baseClassName == 'Element') baseClassName = 'HTMLElement';
+
+  if (extendsTagName == null) {
+    if (baseClassName != 'HTMLElement') {
+      throw new UnsupportedError('Class must provide extendsTag if base '
+          'native class is not HTMLElement');
+    }
+  } else {
+    if (!JS('bool', '(#.createElement(#) instanceof window[#])',
+        document, extendsTagName, baseClassName)) {
+      throw new UnsupportedError('extendsTag does not match base native class');
+    }
+  }
 
   var baseConstructor = JS('=Object', '#[#]', context, baseClassName);
 
diff --git a/tests/html/html.status b/tests/html/html.status
index d3d7586755f..50984d8478e 100644
--- a/tests/html/html.status
+++ b/tests/html/html.status
@@ -411,6 +411,3 @@ async_test: Timeout # Issue 13719: Please triage this failure.
 dromaeo_smoke_test: Fail # Issue 13719: Please triage this failure.
 element_offset_test/offset: Pass, Fail # Issue 13719, 13296
 touchevent_test/supported: Fail # Issue 13719: Please triage this failure.
-
-[ $compiler == dart2js ]
-custom/document_register_type_extensions_test/registration: Fail # Issue 14093
diff --git a/tools/dom/src/dart2js_CustomElementSupport.dart b/tools/dom/src/dart2js_CustomElementSupport.dart
index 6f8aedb2e33..00e17b20569 100644
--- a/tools/dom/src/dart2js_CustomElementSupport.dart
+++ b/tools/dom/src/dart2js_CustomElementSupport.dart
@@ -75,7 +75,18 @@ void _registerCustomElement(context, document, String tag, Type type,
   if (baseClassName == null) {
     throw new ArgumentError(type);
   }
-  if (baseClassName == 'Element') baseClassName = 'HTMLElement';
+
+  if (extendsTagName == null) {
+    if (baseClassName != 'HTMLElement') {
+      throw new UnsupportedError('Class must provide extendsTag if base '
+          'native class is not HTMLElement');
+    }
+  } else {
+    if (!JS('bool', '(#.createElement(#) instanceof window[#])',
+        document, extendsTagName, baseClassName)) {
+      throw new UnsupportedError('extendsTag does not match base native class');
+    }
+  }
 
   var baseConstructor = JS('=Object', '#[#]', context, baseClassName);