diff --git a/backend/open_webui/test/utils/test_misc.py b/backend/open_webui/test/utils/test_misc.py
new file mode 100644
index 0000000000..9ce6289d06
--- /dev/null
+++ b/backend/open_webui/test/utils/test_misc.py
@@ -0,0 +1,33 @@
+import sys
+import types
+
+# Stub lightweight dependencies that misc.py imports at module level so tests
+# can run without a full application bootstrap.
+_env = types.ModuleType('open_webui.env')
+_env.CHAT_STREAM_RESPONSE_CHUNK_MAX_BUFFER_SIZE = 16384
+sys.modules.setdefault('open_webui.env', _env)
+sys.modules.setdefault('mimeparse', types.ModuleType('mimeparse'))
+sys.modules.setdefault('aiohttp', types.ModuleType('aiohttp'))
+
+from open_webui.utils.misc import sanitize_data_for_db  # noqa: E402
+
+
+class TestSanitizeDataForDb:
+    def test_string_null_bytes_removed(self):
+        assert sanitize_data_for_db('a\x00b') == 'ab'
+
+    def test_dict_value_null_bytes_removed(self):
+        result = sanitize_data_for_db({'key': 'val\x00ue'})
+        assert result == {'key': 'value'}
+
+    def test_nested_dict_value_null_bytes_removed(self):
+        result = sanitize_data_for_db({'a': {'b': 'c\x00'}})
+        assert result == {'a': {'b': 'c'}}
+
+    def test_list_value_null_bytes_removed(self):
+        result = sanitize_data_for_db(['a\x00', {'b': 'c\x00'}])
+        assert result == ['a', {'b': 'c'}]
+
+    def test_clean_data_returned_unchanged(self):
+        data = {'key': 'value', 'items': ['a', 'b'], 'num': 42}
+        assert sanitize_data_for_db(data) is data
diff --git a/backend/open_webui/utils/misc.py b/backend/open_webui/utils/misc.py
index 58a038791d..dbf1ef1a30 100644
--- a/backend/open_webui/utils/misc.py
+++ b/backend/open_webui/utils/misc.py
@@ -653,7 +653,7 @@ def sanitize_data_for_db(obj):
     # json.dumps is implemented in C and much faster than a Python-level
     # recursive walk over every leaf string.
     try:
-        if '\x00' not in json.dumps(obj, ensure_ascii=False):
+        if '\\u0000' not in json.dumps(obj):
             return obj
     except (TypeError, ValueError):
         pass