diff --git a/components/style/rule_collector.rs b/components/style/rule_collector.rs
index 6424cc237db..6304a1af2d7 100644
--- a/components/style/rule_collector.rs
+++ b/components/style/rule_collector.rs
@@ -5,7 +5,7 @@
 //! Collects a series of applicable rules for a given element.
 
 use crate::applicable_declarations::{ApplicableDeclarationBlock, ApplicableDeclarationList};
-use crate::dom::{TElement, TShadowRoot};
+use crate::dom::{TElement, TNode, TShadowRoot};
 use crate::properties::{AnimationRules, PropertyDeclarationBlock};
 use crate::rule_tree::{CascadeLevel, ShadowCascadeOrder};
 use crate::selector_map::SelectorMap;
@@ -17,6 +17,43 @@ use selectors::matching::{ElementSelectorFlags, MatchingContext};
 use servo_arc::ArcBorrow;
 use smallvec::SmallVec;
 
+/// This is a bit of a hack so <svg:use> matches the rules of the enclosing
+/// tree.
+///
+/// This function returns the containing shadow host ignoring <svg:use> shadow
+/// trees, since those match the enclosing tree's rules.
+///
+/// Only a handful of places need to really care about this. 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> subtrees are immutable and recreated each time the source tree
+/// changes.
+///
+/// We historically allow cross-document <svg:use> to have these rules applied,
+/// but I think that's not great. Gecko is the only engine supporting that.
+///
+/// See https://github.com/w3c/svgwg/issues/504 for the relevant spec
+/// discussion.
+#[inline]
+pub fn containing_shadow_ignoring_svg_use<E: TElement>(
+    element: E,
+) -> Option<<E::ConcreteNode as TNode>::ConcreteShadowRoot> {
+    let mut shadow = element.containing_shadow()?;
+    loop {
+        let host = shadow.host();
+        let host_is_svg_use_element =
+            host.is_svg_element() && host.local_name() == &*local_name!("use");
+        if !host_is_svg_use_element {
+            return Some(shadow);
+        }
+        debug_assert!(
+            shadow.style_data().is_none(),
+            "We allow no stylesheets in <svg:use> subtrees"
+        );
+        shadow = host.containing_shadow()?;
+    }
+}
+
 /// An object that we use with all the intermediate state needed for the
 /// cascade.
 ///
@@ -213,43 +250,19 @@ where
             return;
         }
 
-        let mut current_containing_shadow = self.rule_hash_target.containing_shadow();
-        while let Some(containing_shadow) = current_containing_shadow {
-            let cascade_data = containing_shadow.style_data();
-            let host = containing_shadow.host();
-            if let Some(map) = cascade_data.and_then(|data| data.normal_rules(self.pseudo_element))
-            {
-                self.collect_rules_in_shadow_tree(host, map, CascadeLevel::SameTreeAuthorNormal);
-            }
-            let host_is_svg_use_element =
-                host.is_svg_element() && host.local_name() == &*local_name!("use");
-            if !host_is_svg_use_element {
-                self.matches_document_author_rules = false;
-                break;
-            }
+        let containing_shadow = containing_shadow_ignoring_svg_use(self.rule_hash_target);
+        let containing_shadow = match containing_shadow {
+            Some(s) => s,
+            None => return,
+        };
 
-            debug_assert!(
-                cascade_data.is_none(),
-                "We allow no stylesheets in <svg:use> subtrees"
-            );
+        self.matches_document_author_rules = false;
 
-            // NOTE(emilio): Hack so <svg:use> matches the rules of the
-            // enclosing tree.
-            //
-            // 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>
-            // subtrees are immutable and recreated each time the source
-            // tree changes.
-            //
-            // We historically allow cross-document <svg:use> to have these
-            // rules applied, but I think that's not great. Gecko is the
-            // only engine supporting that.
-            //
-            // See https://github.com/w3c/svgwg/issues/504 for the relevant
-            // spec discussion.
-            current_containing_shadow = host.containing_shadow();
-            self.matches_document_author_rules = current_containing_shadow.is_none();
+        let cascade_data = containing_shadow.style_data();
+        let host = containing_shadow.host();
+        if let Some(map) = cascade_data.and_then(|data| data.normal_rules(self.pseudo_element))
+        {
+            self.collect_rules_in_shadow_tree(host, map, CascadeLevel::SameTreeAuthorNormal);
         }
     }
 
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 592e4e81081..3815a8a3da6 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -17,7 +17,7 @@ use crate::media_queries::Device;
 use crate::properties::{self, CascadeMode, ComputedValues};
 use crate::properties::{AnimationRules, PropertyDeclarationBlock};
 use crate::rule_cache::{RuleCache, RuleCacheConditions};
-use crate::rule_collector::RuleCollector;
+use crate::rule_collector::{RuleCollector, containing_shadow_ignoring_svg_use};
 use crate::rule_tree::{CascadeLevel, RuleTree, ShadowCascadeOrder, StrongRuleNode, StyleSource};
 use crate::selector_map::{PrecomputedHashMap, PrecomputedHashSet, SelectorMap, SelectorMapEntry};
 use crate::selector_parser::{PerPseudoElementMap, PseudoElement, SelectorImpl, SnapshotMap};
@@ -1187,7 +1187,9 @@ impl Stylist {
             }
         }
 
-        if let Some(shadow) = element.containing_shadow() {
+        // Use the same rules to look for the containing host as we do for rule
+        // collection.
+        if let Some(shadow) = containing_shadow_ignoring_svg_use(element) {
             if let Some(data) = shadow.style_data() {
                 try_find_in!(data);
             }