diff --git a/.changeset/ninety-kids-join.md b/.changeset/ninety-kids-join.md
new file mode 100644
index 0000000..c59469b
--- /dev/null
+++ b/.changeset/ninety-kids-join.md
@@ -0,0 +1,5 @@
+---
+"@chialab/quantum": patch
+---
+
+Upgrade child nodes after realm initialization.
diff --git a/src/Realm.js b/src/Realm.js
index 3ac0b5c..fcdb407 100644
--- a/src/Realm.js
+++ b/src/Realm.js
@@ -277,6 +277,10 @@ export class Realm {
             }
         });
 
+        if (typeof customElements !== 'undefined') {
+            customElements.upgrade(this._fragment);
+        }
+
         this._notifyUpdate();
     }