diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 1320ca354b9..6498ce75fab 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -839,8 +839,8 @@ impl<'a> WindowHelpers for &'a Window {
             Some(parent_node_address) => {
                 let node = from_untrusted_node_address(js_runtime.rt(),
                                                        parent_node_address);
-                let element = ElementCast::to_ref(node.r()).unwrap();
-                Some(Root::from_ref(element))
+                let element = ElementCast::to_ref(node.r());
+                element.map(Root::from_ref)
             }
             None => {
                 None
diff --git a/tests/wpt/metadata-css/css21_dev/html4/first-letter-dynamic-003a.htm.ini b/tests/wpt/metadata-css/css21_dev/html4/first-letter-dynamic-003a.htm.ini
new file mode 100644
index 00000000000..f6c4c8d90d6
--- /dev/null
+++ b/tests/wpt/metadata-css/css21_dev/html4/first-letter-dynamic-003a.htm.ini
@@ -0,0 +1,3 @@
+[first-letter-dynamic-003a.htm]
+  type: reftest
+  expected: FAIL
diff --git a/tests/wpt/metadata-css/css21_dev/html4/first-letter-dynamic-003b.htm.ini b/tests/wpt/metadata-css/css21_dev/html4/first-letter-dynamic-003b.htm.ini
new file mode 100644
index 00000000000..95499887574
--- /dev/null
+++ b/tests/wpt/metadata-css/css21_dev/html4/first-letter-dynamic-003b.htm.ini
@@ -0,0 +1,3 @@
+[first-letter-dynamic-003b.htm]
+  type: reftest
+  expected: FAIL
diff --git a/tests/wpt/metadata-css/css21_dev/html4/run-in-basic-017.htm.ini b/tests/wpt/metadata-css/css21_dev/html4/run-in-basic-017.htm.ini
new file mode 100644
index 00000000000..c7e1e1f65d2
--- /dev/null
+++ b/tests/wpt/metadata-css/css21_dev/html4/run-in-basic-017.htm.ini
@@ -0,0 +1,3 @@
+[run-in-basic-017.htm]
+  type: reftest
+  expected: FAIL
\ No newline at end of file
diff --git a/tests/wpt/metadata/html/semantics/forms/the-input-element/input-type-button.html.ini b/tests/wpt/metadata/html/semantics/forms/the-input-element/input-type-button.html.ini
deleted file mode 100644
index e0fd34f9938..00000000000
--- a/tests/wpt/metadata/html/semantics/forms/the-input-element/input-type-button.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[input-type-button.html]
-  type: testharness
-  [label value]
-    expected: FAIL
-