diff --git a/src/qml/jsruntime/qv4object.cpp b/src/qml/jsruntime/qv4object.cpp
index 6475ec6e06..4d55b15cfa 100644
--- a/src/qml/jsruntime/qv4object.cpp
+++ b/src/qml/jsruntime/qv4object.cpp
@@ -41,8 +41,11 @@ void Object::setInternalClass(Heap::InternalClass *ic)
         // Pick the members of the old IC that are still valid in the new IC.
         // Order them by index in memberData (or inline data).
         Scoped<MemberData> newMembers(scope, MemberData::allocate(scope.engine, ic->size));
-        for (uint i = 0; i < ic->size; ++i)
-            newMembers->set(scope.engine, i, get(ic->nameMap.at(i)));
+        for (uint i = 0; i < ic->size; ++i) {
+            // Note that some members might have been deleted. The key may be invalid.
+            const PropertyKey key = ic->nameMap.at(i);
+            newMembers->set(scope.engine, i, key.isValid() ? get(key) : Encode::undefined());
+        }
 
         p->internalClass.set(scope.engine, ic);
         const uint nInline = p->vtable()->nInlineProperties;
diff --git a/tests/auto/qml/qjsengine/tst_qjsengine.cpp b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
index b6cb4ae0f3..c1c755d843 100644
--- a/tests/auto/qml/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
@@ -310,6 +310,9 @@ private slots:
     void symbolToVariant();
 
     void garbageCollectedObjectMethodBase();
+
+    void deleteDefineCycle();
+
 public:
     Q_INVOKABLE QJSValue throwingCppMethod1();
     Q_INVOKABLE void throwingCppMethod2();
@@ -6302,6 +6305,25 @@ void tst_QJSEngine::garbageCollectedObjectMethodBase()
     }
 }
 
+void tst_QJSEngine::deleteDefineCycle()
+{
+  QJSEngine engine;
+  QStringList stackTrace;
+
+  QJSValue result = engine.evaluate(QString::fromLatin1(R"(
+  let global = ({})
+
+  for (let j = 0; j < 1000; j++) {
+    for (let i = 0; i < 2; i++) {
+      const name = "test" + i
+      delete global[name]
+      Object.defineProperty(global, name, { get() { return 0 }, configurable: true })
+    }
+  }
+  )"), {}, 1, &stackTrace);
+  QVERIFY(stackTrace.isEmpty());
+}
+
 QTEST_MAIN(tst_QJSEngine)
 
 #include "tst_qjsengine.moc"