diff --git a/components/selectors/matching.rs b/components/selectors/matching.rs
index 7c4812cb963..fd4765c2dff 100644
--- a/components/selectors/matching.rs
+++ b/components/selectors/matching.rs
@@ -418,10 +418,6 @@ where
     match combinator {
         Combinator::NextSibling | Combinator::LaterSibling => element.prev_sibling_element(),
         Combinator::Child | Combinator::Descendant => {
-            if element.blocks_ancestor_combinators() {
-                return None;
-            }
-
             match element.parent_element() {
                 Some(e) => return Some(e),
                 None => {},
diff --git a/components/selectors/tree.rs b/components/selectors/tree.rs
index b1c0d41caa8..ef544cc7e4c 100644
--- a/components/selectors/tree.rs
+++ b/components/selectors/tree.rs
@@ -129,11 +129,4 @@ pub trait Element: Sized + Clone + Debug {
     fn ignores_nth_child_selectors(&self) -> bool {
         false
     }
-
-    /// Return true if we want to stop lookup ancestor of the current
-    /// element while matching complex selectors with descendant/child
-    /// combinator.
-    fn blocks_ancestor_combinators(&self) -> bool {
-        false
-    }
 }
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index 035cf0f7821..6cdcf1acd1e 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -856,13 +856,12 @@ impl<'le> GeckoElement<'le> {
     /// Returns true if this node is the shadow root of an use-element shadow tree.
     #[inline]
     fn is_root_of_use_element_shadow_tree(&self) -> bool {
-        if !self.is_root_of_anonymous_subtree() {
+        if !self.as_node().is_in_shadow_tree() {
             return false;
         }
-        match self.parent_element() {
+        match self.containing_shadow_host() {
             Some(e) => {
-                e.local_name() == &*local_name!("use") &&
-                e.is_svg_element()
+                e.is_svg_element() && e.local_name() == &*local_name!("use")
             },
             None => false,
         }
@@ -2332,14 +2331,6 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
     fn ignores_nth_child_selectors(&self) -> bool {
         self.is_root_of_anonymous_subtree()
     }
-
-    #[inline]
-    fn blocks_ancestor_combinators(&self) -> bool {
-        // If this element is the shadow root of an use-element shadow tree,
-        // according to the spec, we should not match rules cross the shadow
-        // DOM boundary.
-        self.is_root_of_use_element_shadow_tree()
-    }
 }
 
 /// A few helpers to help with attribute selectors and snapshotting.
diff --git a/components/style/invalidation/element/element_wrapper.rs b/components/style/invalidation/element/element_wrapper.rs
index 2a31153bd7a..ecbc3b94b78 100644
--- a/components/style/invalidation/element/element_wrapper.rs
+++ b/components/style/invalidation/element/element_wrapper.rs
@@ -367,8 +367,4 @@ where
             .assigned_slot()
             .map(|e| ElementWrapper::new(e, self.snapshot_map))
     }
-
-    fn blocks_ancestor_combinators(&self) -> bool {
-        self.element.blocks_ancestor_combinators()
-    }
 }
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 820f4dbcda7..f4614f945af 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -1261,8 +1261,9 @@ impl Stylist {
 
             if let Some(containing_shadow) = rule_hash_target.containing_shadow() {
                 let cascade_data = containing_shadow.style_data();
+                let host = containing_shadow.host();
                 if let Some(map) = cascade_data.normal_rules(pseudo_element) {
-                    context.with_shadow_host(Some(containing_shadow.host()), |context| {
+                    context.with_shadow_host(Some(host), |context| {
                         map.get_all_matching_rules(
                             element,
                             rule_hash_target,
@@ -1276,7 +1277,26 @@ impl Stylist {
                     shadow_cascade_order += 1;
                 }
 
-                match_document_author_rules = false;
+                // NOTE(emilio): Hack so <svg:use> matches document rules as
+                // expected.
+                //
+                // This is not a problem for invalidation and that kind of stuff
+                // because they still don't match rules based on elements
+                // outside of the shadow tree, and because the <svg:use> subtree
+                // is immutable and recreated each time the source tree changes.
+                //
+                // See: https://github.com/w3c/svgwg/issues/504
+                //
+                // Note that we always resolve URLs against the document, so we
+                // can't get into a nested shadow situation here.
+                //
+                // See: https://github.com/w3c/svgwg/issues/505
+                //
+                let host_is_svg_use =
+                    host.is_svg_element() &&
+                    host.local_name() == &*local_name!("use");
+
+                match_document_author_rules = host_is_svg_use;
             }
         }