diff --git a/poetry.lock b/poetry.lock
index 357a07c..4f09c6e 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1563,13 +1563,13 @@ telegram = ["requests"]
 
 [[package]]
 name = "types-openpyxl"
-version = "3.1.5.20241114"
+version = "3.1.5.20241126"
 description = "Typing stubs for openpyxl"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "types-openpyxl-3.1.5.20241114.tar.gz", hash = "sha256:caeb9aafed8a5ffabdc74f880b148d90375364a1cfe7915d5065c5d79f3fe6a2"},
-    {file = "types_openpyxl-3.1.5.20241114-py3-none-any.whl", hash = "sha256:f2925f595b08f5aef1baa725c9ee40baaf51beb05d98ac150593d3bdd37b1029"},
+    {file = "types_openpyxl-3.1.5.20241126-py3-none-any.whl", hash = "sha256:e50ad5c2dec2c92cca521abed5c039975226e8e76389f17ab0ef813595593fbe"},
+    {file = "types_openpyxl-3.1.5.20241126.tar.gz", hash = "sha256:f599afab19f87aa11672ee675346401d82a0dac71988df9a5411cdb1e7477377"},
 ]
 
 [[package]]
diff --git a/suisa_sendemeldung/suisa_sendemeldung.py b/suisa_sendemeldung/suisa_sendemeldung.py
index 831dbe8..e81fe2f 100644
--- a/suisa_sendemeldung/suisa_sendemeldung.py
+++ b/suisa_sendemeldung/suisa_sendemeldung.py
@@ -28,6 +28,7 @@
 from dateutil.relativedelta import relativedelta
 from iso3901 import ISRC
 from openpyxl import Workbook
+from openpyxl.cell.cell import Cell, MergedCell
 from openpyxl.styles import Border, Font, PatternFill, Side
 from tqdm import tqdm
 
@@ -693,9 +694,10 @@ def get_xlsx(data: Any, args: ArgparseNamespace) -> BytesIO:  # noqa: ANN401
 
     # Try to approximate the required width by finding the longest values per column
     dims: dict[str, int] = {}
-    for row in worksheet.rows:  # type: ignore[assignment]
-        for cell in row:  # type: ignore[assignment]
-            if cell.value:
+    calc_row: tuple[Cell | MergedCell, ...]
+    for calc_row in worksheet.rows:
+        for cell in calc_row:
+            if isinstance(cell, Cell) and cell.value:
                 dims[cell.column_letter] = max(
                     (dims.get(cell.column_letter, 0), len(str(cell.value))),
                 )