diff --git a/autotests/kfilewidgettest.cpp b/autotests/kfilewidgettest.cpp
--- a/autotests/kfilewidgettest.cpp
+++ b/autotests/kfilewidgettest.cpp
@@ -508,6 +508,33 @@
         QCOMPARE(urls.size(), 1);
         QCOMPARE(urls[0], fileUrl);
     }
+
+    void testCreateNestedNewFolders()
+    {
+        // when creating multiple nested new folders in the "save as" dialog, where folders are
+        //created and entered, kdirlister would hit an assert (in reinsert()), bug 408801
+        const QUrl url = QUrl::fromLocalFile(QDir::tempPath()).adjusted(QUrl::StripTrailingSlash);
+        const QString dir = url.toLocalFile();
+        KFileWidget fw(url);
+        fw.setOperationMode(KFileWidget::Saving);
+        fw.setMode(KFile::File);
+        fw.show();
+        fw.activateWindow();
+
+        // create the nested folders
+        for (int i = 1; i < 6; ++i) {
+            fw.dirOperator()->mkdir(QStringLiteral("folder%1").arg(i), true);
+            // simulate the time the user will take to type the new folder name
+            QTest::qWait(1000);
+        }
+
+        QVERIFY(QFile::exists(dir + QStringLiteral("/folder1/folder2/folder3/folder4/folder5")));
+        // check that KFileWidget didn't crash
+        QVERIFY(QTest::qWaitForWindowActive(&fw));
+
+        // cleanup
+        QDir(dir + QStringLiteral("/folder1")).removeRecursively();
+    }
 };
 
 QTEST_MAIN(KFileWidgetTest)
diff --git a/src/core/kcoredirlister_p.h b/src/core/kcoredirlister_p.h
--- a/src/core/kcoredirlister_p.h
+++ b/src/core/kcoredirlister_p.h
@@ -305,9 +305,10 @@
         DirItem *dirItem = dirItemForUrl(parentDir);
         if (dirItem) {
             auto it = std::lower_bound(dirItem->lstItems.begin(), dirItem->lstItems.end(), oldUrl);
-            Q_ASSERT(it != dirItem->lstItems.end());
-            dirItem->lstItems.erase(it);
-            dirItem->insert(item);
+            if (it != dirItem->lstItems.end()) {
+                dirItem->lstItems.erase(it);
+                dirItem->insert(item);
+            }
         }
     }