diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 179cb169c46..de34eb401e0 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -87,6 +87,7 @@ use crate::task::TaskOnce;
 use devtools_traits::AttrInfo;
 use dom_struct::dom_struct;
 use euclid::default::Rect;
+use euclid::default::Size2D;
 use html5ever::serialize;
 use html5ever::serialize::SerializeOpts;
 use html5ever::serialize::TraversalScope;
@@ -3292,7 +3293,25 @@ impl Element {
         {
             return rect;
         }
-        let rect = self.upcast::<Node>().client_rect();
+
+        let mut rect = self.upcast::<Node>().client_rect();
+        let in_quirks_mode = self.node.owner_doc().quirks_mode() == QuirksMode::Quirks;
+
+        if (in_quirks_mode &&
+            self.node.owner_doc().GetBody().as_deref() == self.downcast::<HTMLElement>()) ||
+            (!in_quirks_mode && *self.root_element() == *self)
+        {
+            let viewport_dimensions = self
+                .node
+                .owner_doc()
+                .window()
+                .window_size()
+                .initial_viewport
+                .round()
+                .to_i32();
+            rect.size = Size2D::<i32>::new(viewport_dimensions.width, viewport_dimensions.height);
+        }
+
         self.ensure_rare_data().client_rect = Some(window_from_node(self).cache_layout_value(rect));
         rect
     }
diff --git a/tests/wpt/metadata-layout-2020/css/cssom-view/client-props-root.html.ini b/tests/wpt/metadata-layout-2020/css/cssom-view/client-props-root.html.ini
deleted file mode 100644
index cbdf6bf109c..00000000000
--- a/tests/wpt/metadata-layout-2020/css/cssom-view/client-props-root.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[client-props-root.html]
-  [client* properties on the root element]
-    expected: FAIL
-
diff --git a/tests/wpt/metadata-layout-2020/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini b/tests/wpt/metadata-layout-2020/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini
index 993cbe0ae7f..ccfa50ad607 100644
--- a/tests/wpt/metadata-layout-2020/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini
+++ b/tests/wpt/metadata-layout-2020/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini
@@ -2,9 +2,6 @@
   [scrollingElement in non-quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the HTML body element in quirks mode]
-    expected: FAIL
-
   [scrollLeft/scrollRight of the content in quirks mode]
     expected: FAIL
 
@@ -14,9 +11,6 @@
   [scrollingElement in quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the root element in non-quirks mode]
-    expected: FAIL
-
   [scrollWidth/scrollHeight on the root element in quirks mode]
     expected: FAIL
 
diff --git a/tests/wpt/metadata/css/cssom-view/client-props-root.html.ini b/tests/wpt/metadata/css/cssom-view/client-props-root.html.ini
deleted file mode 100644
index cbdf6bf109c..00000000000
--- a/tests/wpt/metadata/css/cssom-view/client-props-root.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[client-props-root.html]
-  [client* properties on the root element]
-    expected: FAIL
-
diff --git a/tests/wpt/metadata/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini b/tests/wpt/metadata/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini
index 791c8776104..f98497c5a12 100644
--- a/tests/wpt/metadata/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini
+++ b/tests/wpt/metadata/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini
@@ -8,9 +8,6 @@
   [scrollWidth/scrollHeight on the HTML body element in quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the HTML body element in quirks mode]
-    expected: FAIL
-
   [scrollLeft/scrollRight of the content in quirks mode]
     expected: FAIL
 
@@ -20,9 +17,6 @@
   [scrollWidth/scrollHeight on the root element in non-quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the root element in non-quirks mode]
-    expected: FAIL
-
   [scroll() on the HTML body element in non-quirks mode]
     expected: FAIL