diff --git a/app.py b/app.py
index 7654874..61a457a 100644
--- a/app.py
+++ b/app.py
@@ -82,12 +82,29 @@ def upload():
         return render_template('upload.html', error='Ungültige Excel-Datei')
     # mandatory columns
     required = ['question','answer1','answer2','answer3','answer4','correct']
-    if not all(col in df.columns for col in required):
-        return render_template('upload.html', error=f'Fehler in Datei: Fehlende Spalten. Erforderlich: {required}')
+    # ermittelt, welche der benötigten Spalten nicht im DataFrame sind
+    missing = [col for col in required if col not in df.columns]
+    if missing:
+        return render_template(
+            'upload.html',
+            error=f"Fehler in Datei: Fehlende Spalte(n): {', '.join(missing)}"
+        )
     # validate that 'correct' references one of the answer columns
-    if not df['correct'].isin(['answer1','answer2','answer3','answer4']).all():
-        return render_template('upload.html', error='Fehler in Datei: Antwortspalte "correct" muss einen der Werte "answer1", "answer2", "answer3" oder "answer4" enthalten.')
-    # build per-game question list
+    valid_keys = ['answer1','answer2','answer3','answer4']
+    invalid_mask = ~df['correct'].isin(valid_keys)
+    if invalid_mask.any():
+        # finde den ersten Invalid-Eintrag
+        idx = invalid_mask.idxmax()  # DataFrame-Index
+        excel_line = idx + 2         # Header ist Zeile 1
+        bad_value = df.at[idx, 'correct']
+        return render_template(
+            'upload.html',
+            error=(
+                f'Fehler in Zeile {excel_line}: '
+                f'"correct" enthält "{bad_value}", '
+                f'muss einer der Werte {valid_keys} sein.'
+            )
+        )    # build per-game question list
     questions = []
     for _, row in df.iterrows():
         col = row['correct']