diff --git a/CHANGELOG.md b/CHANGELOG.md
index b75a37ce..7e1148cd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## 0.1.9
+
+### Performance
+
+- **Avoid copying uploads during MIME detection**: unknown file types are now detected directly from the existing spooled upload stream while preserving the filename expected by the file-type detector.
+
 ## 0.1.8
 
 ### Features
diff --git a/prepline_general/api/__version__.py b/prepline_general/api/__version__.py
index 93b52aec..4eeb8fc3 100644
--- a/prepline_general/api/__version__.py
+++ b/prepline_general/api/__version__.py
@@ -1 +1 @@
-__version__ = "0.1.8"  # pragma: no cover
+__version__ = "0.1.9"  # pragma: no cover
diff --git a/prepline_general/api/filetypes.py b/prepline_general/api/filetypes.py
index c010afaa..062cff22 100644
--- a/prepline_general/api/filetypes.py
+++ b/prepline_general/api/filetypes.py
@@ -1,6 +1,4 @@
-import os
-from typing import Optional
-from io import BytesIO
+from typing import IO, Any, Optional, cast
 
 from fastapi import HTTPException, UploadFile
 
@@ -8,6 +6,26 @@
 from unstructured.file_utils.model import FileType
 
 
+class _SpooledFileProxy:
+    """Expose a spooled upload as a normal file without copying its complete body.
+
+    `unstructured.detect_filetype()` copies `SpooledTemporaryFile` inputs into a `BytesIO`, even
+    though its detector only seeks and reads small portions. Hiding the concrete type preserves the
+    normal file interface while avoiding that document-sized allocation.
+
+    `name` is set explicitly rather than forwarded: the detector reads `.name` to derive the
+    filename-extension, and a spooled file's own `.name` is the temporary file rather than the
+    uploaded filename.
+    """
+
+    def __init__(self, file: IO[bytes], name: str | None):
+        self._file = file
+        self.name = name
+
+    def __getattr__(self, name: str) -> Any:
+        return getattr(self._file, name)
+
+
 def _remove_optional_info_from_mime_type(content_type: str | None) -> str | None:
     """removes charset information from mime types, e.g.,
     "application/json; charset=utf-8" -> "application/json"
@@ -37,14 +55,14 @@ def get_validated_mimetype(file: UploadFile, content_type_hint: str | None = Non
     filetype = FileType.from_mime_type(content_type)
 
     # If content_type was not specified, use the library to identify the file
-    # We inspect the bytes to do this, so we need to buffer the file
+    # The detector seeks and reads bounded portions of the upload. Proxy the spooled file so the
+    # dependency does not make a complete in-memory `BytesIO` copy first.
     if not filetype or filetype == FileType.UNK:
-        file_buffer = BytesIO(file.file.read())
-        file.file.seek(0)
-
-        file_buffer.name = file.filename
-
-        filetype = detect_filetype(file=file_buffer)
+        file_proxy = cast(IO[bytes], _SpooledFileProxy(file.file, file.filename))
+        try:
+            filetype = detect_filetype(file=file_proxy)
+        finally:
+            file.file.seek(0)
 
     if not filetype.is_partitionable:
         raise HTTPException(
diff --git a/test_general/api/test_filetypes.py b/test_general/api/test_filetypes.py
new file mode 100644
index 00000000..d25b2d42
--- /dev/null
+++ b/test_general/api/test_filetypes.py
@@ -0,0 +1,43 @@
+from tempfile import SpooledTemporaryFile
+
+import pytest
+from fastapi import UploadFile
+
+from prepline_general.api import filetypes
+from unstructured.file_utils.model import FileType
+
+
+def test_unknown_mimetype_is_detected_from_existing_upload_stream(monkeypatch):
+    upload_stream = SpooledTemporaryFile()
+    upload_stream.write(b"sample text")
+    upload_stream.seek(0)
+    upload = UploadFile(file=upload_stream, filename="sample.txt")
+
+    def fake_detect_filetype(*, file):
+        assert file._file is upload_stream
+        assert file.name == "sample.txt"
+        file.seek(4)
+        return FileType.TXT
+
+    monkeypatch.setattr(filetypes, "detect_filetype", fake_detect_filetype)
+
+    assert filetypes.get_validated_mimetype(upload) == "text/plain"
+    assert upload_stream.tell() == 0
+
+
+def test_unknown_mimetype_rewinds_upload_stream_when_detection_fails(monkeypatch):
+    upload_stream = SpooledTemporaryFile()
+    upload_stream.write(b"sample text")
+    upload_stream.seek(0)
+    upload = UploadFile(file=upload_stream, filename="sample.txt")
+
+    def fake_detect_filetype(*, file):
+        file.seek(4)
+        raise RuntimeError("detection failed")
+
+    monkeypatch.setattr(filetypes, "detect_filetype", fake_detect_filetype)
+
+    with pytest.raises(RuntimeError, match="detection failed"):
+        filetypes.get_validated_mimetype(upload)
+
+    assert upload_stream.tell() == 0