diff --git a/example_project/django_mptt_example/models.py b/example_project/django_mptt_example/models.py
index e8d57bf2..5805bafa 100644
--- a/example_project/django_mptt_example/models.py
+++ b/example_project/django_mptt_example/models.py
@@ -28,6 +28,6 @@ def code_or_name(self):
     @property
     def html_code_and_name(self):
         if self.code:
-            return format_html(f"<strong>{self.code}</strong> {self.name}")
+            return format_html("<strong>{}</strong> {}", self.code, self.name)
         else:
-            return format_html(f"<strong>{self.name}</strong>")
+            return format_html("<strong>{}</strong>", self.name)
diff --git a/tox.ini b/tox.ini
index 0c984a33..75e05523 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py311-django32,py311-django40,py311-django41,py311-django42
+envlist = py310-django42,py312-django42,py310-django50,py312-django50,py310-django51,py313-django51
 
 [testenv]
 changedir = {toxinidir}/example_project
@@ -7,11 +7,12 @@ setenv =
     PYTHONWARNINGS = default
 deps =
     -r{toxinidir}/example_project/requirements_test.txt
-    django32: Django>=3.2,<3.3
-    django40: Django>=4.0,<4.1
-    django41: Django>=4.1,<4.2
-    django42: Django==4.2
+    django42: Django>=4.2,<4.3
+    django50: Django>=5.0,<5.1
+    django51: Django>=5.1,<5.2
 commands =
     python -Wd manage.py test django_mptt_example
 basepython =
-    py311: python3.11
+    py310: python3.10
+    py312: python3.12
+    py313: python3.13