diff --git a/html5ever/src/tree_builder/mod.rs b/html5ever/src/tree_builder/mod.rs
index 2310251b..4627b956 100644
--- a/html5ever/src/tree_builder/mod.rs
+++ b/html5ever/src/tree_builder/mod.rs
@@ -1376,6 +1376,25 @@ where
     fn insert_phantom(&self, name: LocalName) -> Handle {
         self.insert_element(Push, ns!(html), name, vec![])
     }
+
+    fn insert_foreign_element(
+        &self,
+        tag: Tag,
+        ns: Namespace,
+        only_add_to_element_stack: bool,
+    ) -> Handle {
+        let adjusted_insertion_location = self.appropriate_place_for_insertion(None);
+        let qname = QualName::new(None, ns, tag.name);
+        let elem = create_element(&self.sink, qname.clone(), tag.attrs.clone());
+
+        if !only_add_to_element_stack {
+            self.insert_at(adjusted_insertion_location, AppendNode(elem.clone()));
+        }
+
+        self.push(&elem);
+
+        elem
+    }
     //§ END
 
     fn should_attach_declarative_shadow(&self, tag: &Tag) -> bool {
@@ -1416,9 +1435,14 @@ where
         is_shadow_root_mode && allow_declarative_shadow_roots && adjusted_current_node_not_topmost
     }
 
-    fn attach_declarative_shadow(&self, tag: &Tag) -> Result<(), String> {
+    fn attach_declarative_shadow(
+        &self,
+        tag: &Tag,
+        shadow_host: &Handle,
+        template: &Handle,
+    ) -> Result<(), String> {
         self.sink
-            .attach_declarative_shadow(self.open_elems.borrow().last().unwrap(), tag.attrs.clone())
+            .attach_declarative_shadow(shadow_host, template, tag.attrs.clone())
     }
 
     fn create_formatting_element_for(&self, tag: Tag) -> Handle {
diff --git a/html5ever/src/tree_builder/rules.rs b/html5ever/src/tree_builder/rules.rs
index f7a76bfd..6c6deacc 100644
--- a/html5ever/src/tree_builder/rules.rs
+++ b/html5ever/src/tree_builder/rules.rs
@@ -160,10 +160,12 @@ where
                     self.template_modes.borrow_mut().push(InTemplate);
 
                     if (self.should_attach_declarative_shadow(&tag)) {
-                        if self.attach_declarative_shadow(&tag).is_err() {
-                            // TODO:
-                            // insert at the adjusted insertion location
-                            // with the result of insert a foreign element for template tag
+                        let shadow_host = self.open_elems.borrow().last().unwrap().clone();
+                        let template = self.insert_foreign_element(tag.clone(), ns!(html), true);
+
+                        if self.attach_declarative_shadow(&tag, &shadow_host, &template).is_err() {
+                            let adjusted_insertion_location = self.appropriate_place_for_insertion(None);
+                            self.insert_at(adjusted_insertion_location, AppendNode(template.clone()));
                         }
                     } else {
                         self.insert_element_for(tag);
diff --git a/markup5ever/interface/tree_builder.rs b/markup5ever/interface/tree_builder.rs
index 139fb6c7..8083a727 100644
--- a/markup5ever/interface/tree_builder.rs
+++ b/markup5ever/interface/tree_builder.rs
@@ -269,6 +269,7 @@ pub trait TreeSink {
     fn attach_declarative_shadow(
         &self,
         _location: &Self::Handle,
+        _template: &Self::Handle,
         _attrs: Vec<Attribute>,
     ) -> Result<(), String> {
         Err(String::from(