diff --git a/src/chameleon/exc.py b/src/chameleon/exc.py
index 3767473..0598897 100644
--- a/src/chameleon/exc.py
+++ b/src/chameleon/exc.py
@@ -314,7 +314,7 @@ def __call__(self) -> str:
         for error in self._errors:
             expression, line, column, filename, exc = error
 
-            if isinstance(exc, UnicodeDecodeError):
+            if isinstance(exc, UnicodeDecodeError) and exc.object is not None:
                 string = safe_native(exc.object)
                 s, marker = compute_source_marker(
                     string, exc.start, string[exc.start:exc.end], LENGTH
diff --git a/src/chameleon/tests/test_templates.py b/src/chameleon/tests/test_templates.py
index 56b5099..3d27633 100644
--- a/src/chameleon/tests/test_templates.py
+++ b/src/chameleon/tests/test_templates.py
@@ -456,6 +456,26 @@ def __init__(self, class_name, bases, namespace):
         exc = create_formatted_exception(Difficult(), Difficult, str)
         assert exc.args == ()
 
+    def test_create_formatted_exception_unicode_error(self):
+        from chameleon.utils import create_formatted_exception
+
+        try:
+            "æøå".encode("utf-8").decode("ascii")
+        except UnicodeDecodeError as exc:
+            inner = exc
+
+        from chameleon.exc import ExceptionFormatter
+        exc = create_formatted_exception(inner, type(inner), str)
+
+        error = "expression", 1, 1, "", exc
+        formatter = ExceptionFormatter([error], {}, {}, repr)
+        exc = create_formatted_exception(
+            NameError('abc'), NameError, formatter
+        )
+
+        formatted = str(exc)
+        assert formatted.startswith(type(inner).__name__)
+
     def test_error_handler_makes_safe_copy(self):
         calls = []
 
diff --git a/src/chameleon/utils.py b/src/chameleon/utils.py
index efda2d8..fa735b7 100644
--- a/src/chameleon/utils.py
+++ b/src/chameleon/utils.py
@@ -225,7 +225,7 @@ def create_formatted_exception(
             inst = cls.__new__(new)
 
         BaseException.__init__(inst, *exc.args)
-        inst.__dict__ = exc.__dict__  # type: ignore[attr-defined]
+        inst.__dict__ = exc.__dict__  # type: ignore[assignment]
 
         return inst
     except ValueError:
diff --git a/tox.ini b/tox.ini
index 6518cb2..0e8d9ab 100644
--- a/tox.ini
+++ b/tox.ini
@@ -25,8 +25,6 @@ deps =
     setuptools
 commands =
     pytest --doctest-modules -W error:"the load_module":DeprecationWarning -W error:"zipimport.zipimporter.load_module":DeprecationWarning -W error:"ast.":DeprecationWarning {posargs}
-extras =
-    test
 setenv =
     LOGNAME=dummy