diff --git a/Libraries/LibWeb/CSS/CSSGroupingRule.cpp b/Libraries/LibWeb/CSS/CSSGroupingRule.cpp
index 9f190779dd..bc1af9c7ad 100644
--- a/Libraries/LibWeb/CSS/CSSGroupingRule.cpp
+++ b/Libraries/LibWeb/CSS/CSSGroupingRule.cpp
@@ -52,12 +52,15 @@ WebIDL::ExceptionOr<u32> CSSGroupingRule::insert_rule(StringView rule, u32 index
 
     // AD-HOC: The spec doesn't say where to set the parent rule, so we'll do it here.
     m_rules->item(index)->set_parent_rule(this);
+    m_parent_style_sheet->invalidate_owners(DOM::StyleInvalidationReason::StyleSheetInsertRule);
     return index;
 }
 
 WebIDL::ExceptionOr<void> CSSGroupingRule::delete_rule(u32 index)
 {
-    return m_rules->remove_a_css_rule(index);
+    TRY(m_rules->remove_a_css_rule(index));
+    m_parent_style_sheet->invalidate_owners(DOM::StyleInvalidationReason::StyleSheetDeleteRule);
+    return {};
 }
 
 void CSSGroupingRule::for_each_effective_rule(TraversalOrder order, Function<void(Web::CSS::CSSRule const&)> const& callback) const
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-nesting/cssom.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-nesting/cssom.txt
index 747c82900f..d70326303a 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/css/css-nesting/cssom.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-nesting/cssom.txt
@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 14 tests
 
-13 Pass
-1 Fail
+14 Pass
 Pass	CSSStyleRule is a CSSGroupingRule
 Pass	Simple CSSOM manipulation of subrules
 Pass	Simple CSSOM manipulation of subrules 1
@@ -17,4 +16,4 @@ Pass	Simple CSSOM manipulation of subrules 8
 Pass	Simple CSSOM manipulation of subrules 9
 Pass	Simple CSSOM manipulation of subrules 10
 Pass	Mutating the selectorText of outer rule invalidates inner rules
-Fail	Manipulation of nested declarations through CSSOM
\ No newline at end of file
+Pass	Manipulation of nested declarations through CSSOM
\ No newline at end of file