diff --git a/components/script/script_task.rs b/components/script/script_task.rs
index 3c54259fc3e..84c9629ff86 100644
--- a/components/script/script_task.rs
+++ b/components/script/script_task.rs
@@ -1594,7 +1594,8 @@ impl ScriptTask {
             let parent_page = self.root_page();
             // TODO(gw): This find will fail when we are sharing script tasks
             // between cross origin iframes in the same TLD.
-            parent_page.find(parent).expect("received load for subpage with missing parent");
+            let parent_page = parent_page.find(parent)
+                                         .expect("received load for subpage with missing parent");
             parent_page.children.borrow_mut().push(page.clone());
         }
 
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index cfa25fec76d..103ccf657ae 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -5637,6 +5637,12 @@
             "url": "/_mozilla/mozilla/iframe_contentDocument.html"
           }
         ],
+        "mozilla/iframe_hierarchy.html": [
+          {
+            "path": "mozilla/iframe_hierarchy.html",
+            "url": "/_mozilla/mozilla/iframe_hierarchy.html"
+          }
+        ],
         "mozilla/img_width_height.html": [
           {
             "path": "mozilla/img_width_height.html",
diff --git a/tests/wpt/mozilla/tests/mozilla/iframe_child1.html b/tests/wpt/mozilla/tests/mozilla/iframe_child1.html
new file mode 100644
index 00000000000..257cc5642cb
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/iframe_child1.html
@@ -0,0 +1 @@
+foo
diff --git a/tests/wpt/mozilla/tests/mozilla/iframe_hierarchy.html b/tests/wpt/mozilla/tests/mozilla/iframe_hierarchy.html
new file mode 100644
index 00000000000..88ec28c229e
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/iframe_hierarchy.html
@@ -0,0 +1,18 @@
+<!doctype html>
+<meta charset="utf-8">
+<title></title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<iframe src="iframe_parent1.html"></iframe>
+<script>
+var t = async_test("iframe content hierarchy is correct");
+function do_test() {
+console.log("whee");
+  t.step(function() {
+    var doc = document.getElementsByTagName("iframe")[0].contentDocument;
+    doc = doc.getElementsByTagName("iframe")[0].contentDocument;
+    assert_equals(doc.body.firstChild.textContent, "foo");
+    t.done();
+  });
+}
+</script>
diff --git a/tests/wpt/mozilla/tests/mozilla/iframe_parent1.html b/tests/wpt/mozilla/tests/mozilla/iframe_parent1.html
new file mode 100644
index 00000000000..146f5b7d529
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/iframe_parent1.html
@@ -0,0 +1 @@
+<iframe src="iframe_child1.html" onload="parent.do_test()"></iframe>
