diff --git a/src/ui/threads.py b/src/ui/threads.py
index 56f7827..6f95d94 100644
--- a/src/ui/threads.py
+++ b/src/ui/threads.py
@@ -247,10 +247,13 @@ class XmlBatchProcessingThread(QThread):
             # Bestimme Ziel-Pfad
             target_xml_path = xml_dir / xml_file_path.name
 
+            # Set aller bereits im Projekt verwendeten Dateinamen — einmalig aufbauen
+            used_filenames = self._collect_project_filenames()
+
             # Prüfe auf Namenskonflikte und generiere ggf. alternativen Namen
             original_name = xml_file_path.name
             counter = 1
-            while target_xml_path.exists() or self._is_filename_used_in_project(Path("xml") / target_xml_path.name):
+            while target_xml_path.exists() or (Path("xml") / target_xml_path.name) in used_filenames:
                 # Generiere alternativen Namen
                 stem = xml_file_path.stem
                 suffix = xml_file_path.suffix
@@ -290,23 +293,20 @@ class XmlBatchProcessingThread(QThread):
         except Exception as e:
             return {"status": "error", "error_msg": str(e)}
 
-    def _is_filename_used_in_project(self, filename: Path) -> bool:
-        """Prüft ob ein Dateiname bereits im Projekt verwendet wird."""
-        if not self.pdf_project.nodes:
-            return False
+    def _collect_project_filenames(self) -> set[Path]:
+        """Gibt ein Set aller im Projekt verwendeten XML-Dateipfade zurück."""
+        result: set[Path] = set()
 
-        def search_recursive(nodes):
+        def collect(nodes):
             for node in nodes:
                 if isinstance(node, XslFile) and node.xmls:
                     for xml_file in node.xmls:
-                        if xml_file.xml == filename:
-                            return True
+                        result.add(xml_file.xml)
                 elif isinstance(node, TreeNode) and node.children:
-                    if search_recursive(node.children):
-                        return True
-            return False
+                    collect(node.children)
 
-        return search_recursive(self.pdf_project.nodes)
+        collect(self.pdf_project.nodes or [])
+        return result
 
     def _update_stats(self, result: dict):
         """Aktualisiert die Statistiken."""