From 7d5b1eebcba019c3e093e8e3614d58c3bce43a88 Mon Sep 17 00:00:00 2001
From: Raphael Michel <michel@rami.io>
Date: Thu, 2 Mar 2023 11:54:49 +0100
Subject: [PATCH] Fix type error in SafeWorksheet

---
 src/pretix/helpers/safe_openpyxl.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/pretix/helpers/safe_openpyxl.py b/src/pretix/helpers/safe_openpyxl.py
index 7d460b5bad..91277f2887 100644
--- a/src/pretix/helpers/safe_openpyxl.py
+++ b/src/pretix/helpers/safe_openpyxl.py
@@ -20,6 +20,7 @@
 # <https://www.gnu.org/licenses/>.
 #
 import re
+import types
 from inspect import isgenerator
 
 from openpyxl import Workbook
@@ -140,9 +141,9 @@ class SafeWorkbook(Workbook):
             # monkeypatch existing sheets
             for s in self._sheets:
                 if self.write_only:
-                    s.append = SafeWriteOnlyWorksheet.append
+                    s.append = types.MethodType(SafeWriteOnlyWorksheet.append, s)
                 else:
-                    s.append = SafeWorksheet.append
+                    s.append = types.MethodType(SafeWorksheet.append, s)
 
     def create_sheet(self, title=None, index=None):
         if self.read_only: