diff --git a/openid-connect-server/src/main/webapp/resources/js/app.js b/openid-connect-server/src/main/webapp/resources/js/app.js
index 8c553f03f..2e6325c12 100644
--- a/openid-connect-server/src/main/webapp/resources/js/app.js
+++ b/openid-connect-server/src/main/webapp/resources/js/app.js
@@ -89,6 +89,9 @@
             // if it's valid and doesn't already exist
             if (model.isValid() && this.collection.where({item: input_value}).length < 1) {
                 this.collection.add(model);
+            } else {
+                // add a visual error indicator
+                $(".control-group", this.el).addClass('error')
             }
         },
 
diff --git a/openid-connect-server/src/main/webapp/resources/template/client.html b/openid-connect-server/src/main/webapp/resources/template/client.html
index 750933961..8cb4e4790 100644
--- a/openid-connect-server/src/main/webapp/resources/template/client.html
+++ b/openid-connect-server/src/main/webapp/resources/template/client.html
@@ -225,7 +225,8 @@
 <script type="text/html" id="tmpl-list-widget">
     <tbody>
     <tr>
-        <td><input type="text" value="" placeholder="<%=(placeholder) ? placeholder : ''%>"></td>
+        <td class="control-group">
+            <input type="text" value="" placeholder="<%=(placeholder) ? placeholder : ''%>"></td>
         <td><button class="btn btn-small" type="button">Add</button></td>
     </tr>
     </tbody>