diff --git a/test/unit/custom-style-late.html b/test/unit/custom-style-late.html
index 6fd7f8ef30..aab52da785 100644
--- a/test/unit/custom-style-late.html
+++ b/test/unit/custom-style-late.html
@@ -29,11 +29,10 @@
   <template id="late">
   <custom-style>
     <style is="custom-style">
-      :root {
+      html {
         --cs-blue: {
           border: 8px solid blue;
-        }
-        ;
+        };
       }
     </style>
   </custom-style>
@@ -52,10 +51,13 @@
         });
         var template = document.querySelector('template#late');
         document.body.appendChild(document.importNode(template.content, true));
-        setTimeout(function() {
-          assertComputed(input, '8px');
-          done();
-        }, 125);
+        // wait 2 rounds of `afterNextRender` as `<custom-style>` boots asynchronously
+        Polymer.RenderStatus.afterNextRender(null, function() {
+          Polymer.RenderStatus.afterNextRender(null, function() {
+            assertComputed(input, '8px');
+            done();
+          });
+        });
       });
 
     });