diff --git a/components/selectors/matching.rs b/components/selectors/matching.rs
index f648594db04..7b505779315 100644
--- a/components/selectors/matching.rs
+++ b/components/selectors/matching.rs
@@ -338,8 +338,7 @@ pub fn matches_compound_selector<E>(
 where
     E: Element
 {
-    debug_assert_ne!(from_offset, 0);
-    if cfg!(debug_assertions) {
+    if cfg!(debug_assertions) && from_offset != 0 {
         selector.combinator_at_parse_order(from_offset - 1); // This asserts.
     }
 
diff --git a/components/style/invalidation/element/invalidator.rs b/components/style/invalidation/element/invalidator.rs
index 99e42e6d860..359617466d9 100644
--- a/components/style/invalidation/element/invalidator.rs
+++ b/components/style/invalidation/element/invalidator.rs
@@ -112,6 +112,10 @@ impl Invalidation {
     /// Whether this invalidation is effective for the next sibling or
     /// descendant after us.
     fn effective_for_next(&self) -> bool {
+        if self.offset == 0 {
+            return true;
+        }
+
         // TODO(emilio): For pseudo-elements this should be mostly false, except
         // for the weird pseudos in <input type="number">.
         //
@@ -124,6 +128,10 @@ impl Invalidation {
     }
 
     fn kind(&self) -> InvalidationKind {
+        if self.offset == 0 {
+            return InvalidationKind::Descendant;
+        }
+
         if self.selector.combinator_at_parse_order(self.offset - 1).is_ancestor() {
             InvalidationKind::Descendant
         } else {