diff --git a/cmd/wasm/components.go b/cmd/wasm/components.go
index a982d52..faab087 100644
--- a/cmd/wasm/components.go
+++ b/cmd/wasm/components.go
@@ -60,6 +60,7 @@ func jsStringLiteral(s string) string {
 func customElementClassSource(tag, slot string) string {
 	className := tagToClassName(tag)
 	return "class " + className + " extends HTMLElement {" +
+		"#shadow;" +
 		"constructor(){super();this.#shadow=this.attachShadow({mode:\"closed\"});}" +
 		"connectedCallback(){this.#shadow.textContent=\"\";const slot=this.getAttribute(\"data-slot\")||" + jsStringLiteral(slot) + ";" +
 		"this.dispatchEvent(new CustomEvent(\"wc-ready\",{detail:{tag:" + jsStringLiteral(tag) + ",slot}}));}" +
diff --git a/cmd/wasm/register_test.go b/cmd/wasm/register_test.go
index 0dfc025..eaf57e0 100644
--- a/cmd/wasm/register_test.go
+++ b/cmd/wasm/register_test.go
@@ -63,6 +63,7 @@ func TestCustomElementClassSource(t *testing.T) {
 	src := customElementClassSource(`nav-bar`, `H`)
 
 	assert.Contains(t, src, `class NavBar extends HTMLElement`)
+	assert.Contains(t, src, `#shadow;`)
 	assert.Contains(t, src, `mode:"closed"`)
 	assert.Contains(t, src, `#shadow`)
 	assert.Contains(t, src, `data-slot`)