diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index e5249a52b8f..fe96fd78ad8 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -2415,6 +2415,9 @@ impl CascadeData {
         if let Some(ref mut slotted_rules) = self.slotted_rules {
             slotted_rules.clear();
         }
+        if let Some(ref mut host_rules) = self.host_rules {
+            host_rules.clear();
+        }
         self.animations.clear();
         self.extra_data.clear();
         self.rules_source_order = 0;
@@ -2440,6 +2443,9 @@ impl CascadeData {
         if let Some(ref slotted_rules) = self.slotted_rules {
             slotted_rules.add_size_of(ops, sizes);
         }
+        if let Some(ref host_rules) = self.host_rules {
+            host_rules.add_size_of(ops, sizes);
+        }
         sizes.mInvalidationMap += self.invalidation_map.size_of(ops);
         sizes.mRevalidationSelectors += self.selectors_for_cache_revalidation.size_of(ops);
         sizes.mOther += self.animations.size_of(ops);