diff --git a/lib/phoenix_live_view/test/dom.ex b/lib/phoenix_live_view/test/dom.ex
index 6344708bc0..9064f7dde6 100644
--- a/lib/phoenix_live_view/test/dom.ex
+++ b/lib/phoenix_live_view/test/dom.ex
@@ -37,6 +37,9 @@ defmodule Phoenix.LiveViewTest.DOM do
     detect_duplicate_ids(rest, ids)
   end
 
+  # ignore declarations
+  defp detect_duplicate_ids({:pi, _type, _attrs}, seen_ids), do: seen_ids
+
   defp detect_duplicate_ids({_tag_name, _attrs, children} = node, ids) do
     case Floki.attribute(node, "id") do
       [id] ->
diff --git a/test/phoenix_live_view/test/dom_test.exs b/test/phoenix_live_view/test/dom_test.exs
index aa1d48143d..142eefaa43 100644
--- a/test/phoenix_live_view/test/dom_test.exs
+++ b/test/phoenix_live_view/test/dom_test.exs
@@ -292,4 +292,24 @@ defmodule Phoenix.LiveViewTest.DOMTest do
                %{s: "bar", streams: []}
     end
   end
+
+  describe "parse" do
+    test "detects duplicate ids" do
+      assert_raise RuntimeError, fn ->
+        DOM.parse("""
+        <div id="foo">
+          <div id="foo"></div>
+        </div>
+        """)
+      end
+    end
+
+    test "handles declarations (issue #3594)" do
+      assert DOM.parse("""
+             <div id="foo">
+               <?xml version="1.0" standalone="yes"?>
+             </div>
+             """)
+    end
+  end
 end