diff --git a/tests/unit/test_file_processor.py b/tests/unit/test_file_processor.py
index b5e8323..1323011 100644
--- a/tests/unit/test_file_processor.py
+++ b/tests/unit/test_file_processor.py
@@ -27,15 +27,16 @@ def test_read_lines_splits_lines():
                for line in lines)
 
 
-def lines_from_file(tmpdir, lines):
+def lines_from_file(tmpdir, contents):
     f = tmpdir.join('f.py')
-    f.write(''.join(lines))
+    # be careful to write the bytes exactly to avoid newline munging
+    f.write_binary(contents)
     return processor.FileProcessor(f.strpath, options_from()).lines
 
 
 def test_read_lines_universal_newlines(tmpdir):
     r"""Verify that line endings are translated to \n."""
-    lines = lines_from_file(tmpdir, ['# coding: utf-8\r\n', 'x = 1\r\n'])
+    lines = lines_from_file(tmpdir, b'# coding: utf-8\r\nx = 1\r\n')
     assert lines == ['# coding: utf-8\n', 'x = 1\n']
 
 
@@ -43,13 +44,13 @@ def test_read_lines_incorrect_utf_16(tmpdir):
     """Verify that a file which incorrectly claims it is utf16 is still read
     as latin-1.
     """
-    lines = lines_from_file(tmpdir, ['# coding: utf16\n', 'x = 1\n'])
+    lines = lines_from_file(tmpdir, b'# coding: utf16\nx = 1\n')
     assert lines == ['# coding: utf16\n', 'x = 1\n']
 
 
 def test_read_lines_unknown_encoding(tmpdir):
     """Verify that an unknown encoding is still read as latin-1."""
-    lines = lines_from_file(tmpdir, ['# coding: fake-encoding\n', 'x = 1\n'])
+    lines = lines_from_file(tmpdir, b'# coding: fake-encoding\nx = 1\n')
     assert lines == ['# coding: fake-encoding\n', 'x = 1\n']