diff --git a/test/cli/samples/custom-element/expected/Main.js b/test/cli/samples/custom-element/expected/Main.js
index 40865a2c81..179ab07695 100644
--- a/test/cli/samples/custom-element/expected/Main.js
+++ b/test/cli/samples/custom-element/expected/Main.js
@@ -67,7 +67,9 @@ assign(Main.prototype, {
 	}
 });
 
-customElements.define("my-element", Main);
+if (!customElements.get("my-element")) {
+	customElements.define("my-element", Main);
+}
 
 Main.prototype._recompute = noop;
 
diff --git a/test/js/samples/css-shadow-dom-keyframes/expected.js b/test/js/samples/css-shadow-dom-keyframes/expected.js
index e9375bf007..02af319208 100644
--- a/test/js/samples/css-shadow-dom-keyframes/expected.js
+++ b/test/js/samples/css-shadow-dom-keyframes/expected.js
@@ -59,5 +59,7 @@ assign(SvelteComponent.prototype, {
 	}
 });
 
-customElements.define("custom-element", SvelteComponent);
+if (!customElements.get("custom-element")) {
+	customElements.define("custom-element", SvelteComponent);
+}
 export default SvelteComponent;
\ No newline at end of file