diff --git a/sentry_sdk/utils.py b/sentry_sdk/utils.py
index 7a8917fecc..0fead48377 100644
--- a/sentry_sdk/utils.py
+++ b/sentry_sdk/utils.py
@@ -1501,7 +1501,7 @@ def qualname_from_function(func):
 
     # Python 3: methods, functions, classes
     if func_qualname is not None:
-        if hasattr(func, "__module__"):
+        if hasattr(func, "__module__") and isinstance(func.__module__, str):
             func_qualname = func.__module__ + "." + func_qualname
         func_qualname = prefix + func_qualname + suffix
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 6e01bb4f3a..894638bf4d 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -951,3 +951,23 @@ def test_format_timestamp_naive():
     # Ensure that some timestamp is returned, without error. We currently treat these as local time, but this is an
     # implementation detail which we should not assert here.
     assert re.fullmatch(timestamp_regex, format_timestamp(datetime_object))
+
+
+def test_qualname_from_function_inner_function():
+    def test_function(): ...
+
+    assert (
+        sentry_sdk.utils.qualname_from_function(test_function)
+        == "tests.test_utils.test_qualname_from_function_inner_function.<locals>.test_function"
+    )
+
+
+def test_qualname_from_function_none_name():
+    def test_function(): ...
+
+    test_function.__module__ = None
+
+    assert (
+        sentry_sdk.utils.qualname_from_function(test_function)
+        == "test_qualname_from_function_none_name.<locals>.test_function"
+    )