diff --git a/Userland/Libraries/LibWeb/CSS/Parser/SelectorParsing.cpp b/Userland/Libraries/LibWeb/CSS/Parser/SelectorParsing.cpp
index 303989800a6..85da12d7c7c 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/SelectorParsing.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/SelectorParsing.cpp
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2018-2022, Andreas Kling <andreas@ladybird.org>
  * Copyright (c) 2020-2021, the SerenityOS developers.
- * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2021-2024, Sam Atkins <sam@ladybird.org>
  * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
  * Copyright (c) 2022, MacDue <macdue@dueutil.tech>
  *
@@ -662,6 +662,10 @@ Parser::ParseErrorOr<Optional<Selector::SimpleSelector>> Parser::parse_simple_se
         case '*':
             // Handled already
             VERIFY_NOT_REACHED();
+        case '&':
+            return Selector::SimpleSelector {
+                .type = Selector::SimpleSelector::Type::Nesting,
+            };
         case '.': {
             if (peek_token_ends_selector())
                 return ParseError::SyntaxError;
diff --git a/Userland/Libraries/LibWeb/CSS/Selector.cpp b/Userland/Libraries/LibWeb/CSS/Selector.cpp
index c1b41ed9e93..4b94cced78e 100644
--- a/Userland/Libraries/LibWeb/CSS/Selector.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Selector.cpp
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <andreas@ladybird.org>
- * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2021-2024, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -153,6 +153,9 @@ u32 Selector::specificity() const
             case SimpleSelector::Type::Universal:
                 // ignore the universal selector
                 break;
+            case SimpleSelector::Type::Nesting:
+                // We should have replaced this already
+                VERIFY_NOT_REACHED();
             }
         }
     }
@@ -325,8 +328,9 @@ String Selector::SimpleSelector::serialize() const
     case Selector::SimpleSelector::Type::PseudoElement:
         // Note: Pseudo-elements are dealt with in Selector::serialize()
         break;
-    default:
-        dbgln("FIXME: Unsupported simple selector serialization for type {}", to_underlying(type));
+    case Type::Nesting:
+        // AD-HOC: Not in spec yet.
+        s.append('&');
         break;
     }
     return MUST(s.to_string());
diff --git a/Userland/Libraries/LibWeb/CSS/Selector.h b/Userland/Libraries/LibWeb/CSS/Selector.h
index 2aab0bd35c1..36f3c46ed72 100644
--- a/Userland/Libraries/LibWeb/CSS/Selector.h
+++ b/Userland/Libraries/LibWeb/CSS/Selector.h
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <andreas@ladybird.org>
- * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2021-2024, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -23,7 +23,7 @@ class Selector : public RefCounted<Selector> {
 public:
     class PseudoElement {
     public:
-        enum class Type {
+        enum class Type : u8 {
             Before,
             After,
             FirstLine,
@@ -83,7 +83,7 @@ public:
     };
 
     struct SimpleSelector {
-        enum class Type {
+        enum class Type : u8 {
             Universal,
             TagName,
             Id,
@@ -91,6 +91,7 @@ public:
             Attribute,
             PseudoClass,
             PseudoElement,
+            Nesting,
         };
 
         struct ANPlusBPattern {
diff --git a/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp b/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
index 70713d35942..c109dd2462f 100644
--- a/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
+++ b/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2018-2024, Andreas Kling <andreas@ladybird.org>
- * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2021-2024, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -742,9 +742,11 @@ static inline bool matches(CSS::Selector::SimpleSelector const& component, Optio
     case CSS::Selector::SimpleSelector::Type::PseudoElement:
         // Pseudo-element matching/not-matching is handled in the top level matches().
         return true;
-    default:
+    case CSS::Selector::SimpleSelector::Type::Nesting:
+        // We should only try to match selectors that have been absolutized!
         VERIFY_NOT_REACHED();
     }
+    VERIFY_NOT_REACHED();
 }
 
 static inline bool matches(CSS::Selector const& selector, Optional<CSS::CSSStyleSheet const&> style_sheet_for_rule, int component_list_index, DOM::Element const& element, JS::GCPtr<DOM::Element const> shadow_host, JS::GCPtr<DOM::ParentNode const> scope, SelectorKind selector_kind)
diff --git a/Userland/Libraries/LibWeb/Dump.cpp b/Userland/Libraries/LibWeb/Dump.cpp
index 38979baa1d8..68bd8f0243b 100644
--- a/Userland/Libraries/LibWeb/Dump.cpp
+++ b/Userland/Libraries/LibWeb/Dump.cpp
@@ -503,6 +503,9 @@ void dump_selector(StringBuilder& builder, CSS::Selector const& selector, int in
             case CSS::Selector::SimpleSelector::Type::PseudoElement:
                 type_description = "PseudoElement";
                 break;
+            case CSS::Selector::SimpleSelector::Type::Nesting:
+                type_description = "Nesting";
+                break;
             }
 
             builder.appendff("{}:", type_description);