diff --git a/components/script/dom/resizeobserver.rs b/components/script/dom/resizeobserver.rs
index b2bbaa52716..b685151c153 100644
--- a/components/script/dom/resizeobserver.rs
+++ b/components/script/dom/resizeobserver.rs
@@ -296,7 +296,7 @@ impl ResizeObservation {
 /// <https://drafts.csswg.org/resize-observer/#calculate-depth-for-node>
 fn calculate_depth_for_node(target: &Element) -> ResizeObservationDepth {
     let node = target.upcast::<Node>();
-    let depth = node.ancestors().count();
+    let depth = node.inclusive_ancestors_in_flat_tree().count() - 1;
     ResizeObservationDepth(depth)
 }
 
diff --git a/tests/wpt/meta/resize-observer/calculate-depth-for-node.html.ini b/tests/wpt/meta/resize-observer/calculate-depth-for-node.html.ini
deleted file mode 100644
index 4e3c57f9422..00000000000
--- a/tests/wpt/meta/resize-observer/calculate-depth-for-node.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[calculate-depth-for-node.html]
-  expected: ERROR
-
-  ["Calculate depth for node" algorithm with Shadow DOM]
-    expected: FAIL