diff --git a/src/report_generator.py b/src/report_generator.py
index 39fe0e1..a794ed3 100644
--- a/src/report_generator.py
+++ b/src/report_generator.py
@@ -78,6 +78,7 @@ def _prepare_timeline(articles: list) -> list:
     timeline = []
     for art in articles:
         pub = art.get("published_at") or art.get("collected_at") or ""
+        pub = str(pub) if pub else ""
         headline = art.get("headline_de") or art.get("headline") or "Ohne Titel"
         source = art.get("source") or ""
         if pub:
@@ -349,7 +350,7 @@ async def generate_pdf(
 
     # Artikel pub_date aufbereiten
     for art in articles:
-        pub = art.get("published_at") or art.get("collected_at") or ""
+        pub = str(art.get("published_at") or art.get("collected_at") or "")
         try:
             dt = datetime.fromisoformat(pub.replace("Z", "+00:00"))
             art["pub_date"] = dt.strftime("%d.%m.%Y")
@@ -534,7 +535,7 @@ async def generate_docx(
                 row[0].text = art.get("headline_de") or art.get("headline") or "Ohne Titel"
                 row[1].text = art.get("source") or ""
                 row[2].text = (art.get("language") or "de").upper()
-                pub = art.get("published_at") or art.get("collected_at") or ""
+                pub = str(art.get("published_at") or art.get("collected_at") or "")
                 try:
                     dt = datetime.fromisoformat(pub.replace("Z", "+00:00"))
                     row[3].text = dt.strftime("%d.%m.%Y")