diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
index fd7a1655a3..0b63e9af4d 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
@@ -457,17 +457,34 @@ NonnullRefPtr<DOM::Element> HTMLDocumentParser::create_element_for(const HTMLTok
     return element;
 }
 
-RefPtr<DOM::Element> HTMLDocumentParser::insert_foreign_element(const HTMLToken& token, const FlyString& namespace_)
+// https://html.spec.whatwg.org/multipage/parsing.html#insert-a-foreign-element
+NonnullRefPtr<DOM::Element> HTMLDocumentParser::insert_foreign_element(const HTMLToken& token, const FlyString& namespace_)
 {
     auto adjusted_insertion_location = find_appropriate_place_for_inserting_node();
+
+    // FIXME: Pass in adjusted_insertion_location.parent as the intended parent.
     auto element = create_element_for(token, namespace_);
-    // FIXME: Check if it's possible to insert `element` at `adjusted_insertion_location`
-    adjusted_insertion_location.parent->insert_before(element, adjusted_insertion_location.insert_before_sibling);
+
+    auto pre_insertion_validity = adjusted_insertion_location.parent->ensure_pre_insertion_validity(element, adjusted_insertion_location.insert_before_sibling);
+
+    // NOTE: If it's not possible to insert the element at the adjusted insertion location, the element is simply dropped.
+    if (!pre_insertion_validity.is_exception()) {
+        if (!m_parsing_fragment) {
+            // FIXME: push a new element queue onto element's relevant agent's custom element reactions stack.
+        }
+
+        adjusted_insertion_location.parent->insert_before(element, adjusted_insertion_location.insert_before_sibling);
+
+        if (!m_parsing_fragment) {
+            // FIXME: pop the element queue from element's relevant agent's custom element reactions stack, and invoke custom element reactions in that queue.
+        }
+    }
+
     m_stack_of_open_elements.push(element);
     return element;
 }
 
-RefPtr<DOM::Element> HTMLDocumentParser::insert_html_element(const HTMLToken& token)
+NonnullRefPtr<DOM::Element> HTMLDocumentParser::insert_html_element(const HTMLToken& token)
 {
     return insert_foreign_element(token, Namespace::HTML);
 }
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.h b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.h
index 4abbb74b72..4f1c4f2214 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.h
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.h
@@ -127,8 +127,8 @@ private:
 
     DOM::Text* find_character_insertion_node();
     void flush_character_insertions();
-    RefPtr<DOM::Element> insert_foreign_element(const HTMLToken&, const FlyString&);
-    RefPtr<DOM::Element> insert_html_element(const HTMLToken&);
+    NonnullRefPtr<DOM::Element> insert_foreign_element(const HTMLToken&, const FlyString&);
+    NonnullRefPtr<DOM::Element> insert_html_element(const HTMLToken&);
     DOM::Element& current_node();
     DOM::Element& adjusted_current_node();
     DOM::Element& node_before_current_node();