diff --git a/packages/markitdown/src/markitdown/converters/_zip_converter.py b/packages/markitdown/src/markitdown/converters/_zip_converter.py
index f87e6c890..3d388a781 100644
--- a/packages/markitdown/src/markitdown/converters/_zip_converter.py
+++ b/packages/markitdown/src/markitdown/converters/_zip_converter.py
@@ -90,7 +90,12 @@ def convert(
         stream_info: StreamInfo,
         **kwargs: Any,  # Options to pass to the converter
     ) -> DocumentConverterResult:
-        file_path = stream_info.url or stream_info.local_path or stream_info.filename
+        file_path = (
+            stream_info.url
+            or stream_info.local_path
+            or stream_info.filename
+            or "(unknown)"
+        )
         md_content = f"Content from the zip file `{file_path}`:\n\n"
 
         with zipfile.ZipFile(file_stream, "r") as zipObj:
diff --git a/packages/markitdown/tests/test_module_misc.py b/packages/markitdown/tests/test_module_misc.py
index 39a8c20d5..7001b42b9 100644
--- a/packages/markitdown/tests/test_module_misc.py
+++ b/packages/markitdown/tests/test_module_misc.py
@@ -5,6 +5,7 @@
 import os
 import re
 import shutil
+import zipfile
 from types import SimpleNamespace
 import pytest
 from unittest.mock import MagicMock
@@ -785,6 +786,24 @@ def test_markitdown_llm() -> None:
     validate_strings(result, PPTX_TEST_STRINGS)
 
 
+def test_zip_stream_no_filename_header() -> None:
+    """Regression test: ZipConverter must not render the literal string 'None'
+    in the output header when the stream has no associated URL, local path, or
+    filename (e.g. when called via convert_stream() without stream_info)."""
+    markitdown = MarkItDown()
+
+    buf = io.BytesIO()
+    with zipfile.ZipFile(buf, "w") as zf:
+        zf.writestr("hello.txt", "Hello world")
+    buf.seek(0)
+
+    result = markitdown.convert_stream(
+        buf, stream_info=StreamInfo(mimetype="application/zip")
+    )
+    assert result.markdown.startswith("Content from the zip file `(unknown)`:\n\n")
+    assert "Hello world" in result.markdown
+
+
 def test_ipynb_accepts_non_ascii() -> None:
     """IpynbConverter.accepts() must not raise on non-ASCII binary content."""
     from markitdown.converters._ipynb_converter import IpynbConverter