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 4d62e4919..5c99d08a8 100644
--- a/packages/markitdown/tests/test_module_misc.py
+++ b/packages/markitdown/tests/test_module_misc.py
@@ -3,6 +3,7 @@
 import os
 import re
 import shutil
+import zipfile
 import pytest
 from unittest.mock import MagicMock
 
@@ -532,6 +533,27 @@ 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 (
+        "None" not in result.markdown
+    ), f"Header must not contain literal 'None'; got: {result.markdown[:120]!r}"
+    assert "Content from the zip file" in result.markdown
+    assert "Hello world" in result.markdown
+
+
 if __name__ == "__main__":
     """Runs this file's tests from the command line."""
     for test in [