diff --git a/README.rst b/README.rst
index 2822f0c..9444856 100644
--- a/README.rst
+++ b/README.rst
@@ -71,6 +71,11 @@ Also you can pass an opened file:
     with open('file.html') as f:
         pdfkit.from_file(f, 'out.pdf')
 
+Text streams are encoded as UTF-8. Binary streams (including ``io.BytesIO``
+and files opened with ``'rb'``) are passed through without changing their bytes.
+The caller retains ownership of the input stream.
+
+
 If you wish to further process generated PDF, you can read it to a variable:
 
 .. code-block:: python
diff --git a/pdfkit/pdfkit.py b/pdfkit/pdfkit.py
index 88b3c92..7ebe4eb 100644
--- a/pdfkit/pdfkit.py
+++ b/pdfkit/pdfkit.py
@@ -183,7 +183,9 @@ def to_pdf(self, path=None):
         if self.source.isString() or (self.source.isFile() and self.css):
             input = self.source.to_s().encode('utf-8')
         elif self.source.isFileObj():
-            input = self.source.source.read().encode('utf-8')
+            input = self.source.source.read()
+            if isinstance(input, str):
+                input = input.encode('utf-8')
         else:
             input = None
 
diff --git a/tests/test_file_stream_input.py b/tests/test_file_stream_input.py
new file mode 100644
index 0000000..e9856ce
--- /dev/null
+++ b/tests/test_file_stream_input.py
@@ -0,0 +1,36 @@
+import io
+import sys
+import tempfile
+import unittest
+from unittest.mock import Mock, patch
+
+import pdfkit
+
+
+class FileStreamInputTests(unittest.TestCase):
+    def convert(self, stream, expected):
+        config = pdfkit.configuration(wkhtmltopdf=sys.executable)
+        process = Mock(returncode=0)
+        process.communicate.return_value = (b'%PDF-test-output', b'')
+        with patch('pdfkit.pdfkit.subprocess.Popen', return_value=process):
+            output = pdfkit.from_file(stream, configuration=config)
+        self.assertEqual(output, b'%PDF-test-output')
+        process.communicate.assert_called_once_with(input=expected)
+        self.assertFalse(stream.closed)
+
+    def test_binary_memory_stream(self):
+        data = '<p>café</p>'.encode('utf-8')
+        self.convert(io.BytesIO(data), data)
+
+    def test_binary_file_preserves_declared_encoding(self):
+        data = b'<meta charset="iso-8859-1"><p>caf\xe9</p>'
+        with tempfile.TemporaryFile('w+b') as stream:
+            stream.write(data)
+            stream.seek(0)
+            self.convert(stream, data)
+
+    def test_text_stream_is_encoded_as_utf8(self):
+        self.convert(io.StringIO('<p>café</p>'), '<p>café</p>'.encode('utf-8'))
+
+    def test_empty_binary_stream(self):
+        self.convert(io.BytesIO(b''), b'')