Index: Lib/doctest.py
===================================================================
--- Lib/doctest.py	(revision 82984)
+++ Lib/doctest.py	(working copy)
@@ -204,6 +204,7 @@
         raise TypeError("Expected a module, string, or None")
 
 def _load_testfile(filename, package, module_relative, encoding):
+    file_contents = None
     if module_relative:
         package = _normalize_module(package, 3)
         filename = _module_relative_path(package, filename)
@@ -212,9 +213,20 @@
                 file_contents = package.__loader__.get_data(filename)
                 file_contents = file_contents.decode(encoding)
                 # get_data() opens files as 'rb', so one must do the equivalent
-                # conversion as universal newlines would do.
-                return file_contents.replace(os.linesep, '\n'), filename
-    return open(filename, encoding=encoding).read(), filename
+                # conversion as universal newlines would do -- see below.
+    if file_contents is None:
+        # Universal newline mode is the default, no need for mode='rU'
+        f = open(filename, encoding=encoding)
+        file_contents = f.read()
+        # However, we still need to check to make sure universal newlines are enabled
+        if hasattr(f, 'newlines'):
+            # Universal newlines are enabled, we're OK
+            return file_contents, filename
+    # If we get here, we need to do the universal newline conversion ourselves;
+    # we have two possible cases and we need to do them in the right order
+    for linesep in ('\r\n', '\r'):
+        file_contents = file_contents.replace(linesep, '\n')
+    return file_contents, filename
 
 def _indent(s, indent=4):
     """
Index: Lib/test/test_doctest.py
===================================================================
--- Lib/test/test_doctest.py	(revision 82984)
+++ Lib/test/test_doctest.py	(working copy)
@@ -2388,6 +2388,13 @@
     TestResults(failed=0, attempted=2)
     >>> doctest.master = None  # Reset master.
     >>> sys.argv = save_argv
+
+We use a helper script to test for correct newline handling in
+the _load_testfile function:
+
+    >>> from test import doctest_testfile
+    >>> doctest_testfile.run()
+    >>> doctest.master = None  # Reset master.
 """
 
 def test_testmod(): r"""
Index: Lib/test/doctest_testfile.py
===================================================================
--- Lib/test/doctest_testfile.py	(revision 0)
+++ Lib/test/doctest_testfile.py	(revision 0)
@@ -0,0 +1,71 @@
+"""
+Test script to exercise all code paths and parameter
+combinations of _load_testfile in doctest.py
+
+To be called from test_doctest.py
+"""
+
+import sys
+import os
+import doctest
+import test
+from test import test_importhooks
+
+# We use the directory where the 'test' package lives as
+# our "current directory" for loading test files (this is
+# so the test is independent of the current working dir)
+curdir = test.__path__[0]
+curname = "doctest_testfile"
+rootpath, pkgname = os.path.split(curdir)
+hookpkgname = "hooktestpackage"
+txtfile = curname + ".txt"
+
+# Need helper classes for the package loader test, code cribbed
+# shamelessly from test_importhooks
+class PackageLoaderTestImporter(test_importhooks.PathImporter):
+    def __init__(self, path=''):
+        self.path = path
+    def get_data(self, path):
+        return open(os.path.join(self.path, path), mode='rb').read()
+
+class InstallHook:
+    def __init__(self, pkgname):
+        self.pkgname = pkgname
+        self.path = sys.path[:]
+        self.meta_path = sys.meta_path[:]
+        self.path_hooks = sys.path_hooks[:]
+        sys.path_importer_cache.clear()
+        self.modules_before = sys.modules.copy()
+        self.importer = PackageLoaderTestImporter(path=curdir)
+        sys.meta_path.append(self.importer)
+    
+    def remove(self):
+        sys.path[:] = self.path
+        sys.meta_path[:] = self.meta_path
+        sys.path_hooks[:] = self.path_hooks
+        sys.path_importer_cache.clear()
+        sys.modules.clear()
+        sys.modules.update(self.modules_before)
+        del self.importer
+
+def run():
+    # First test the default (module_relative=True, no package)
+    doctest.testfile(txtfile)
+    doctest.master = None
+    
+    # Now try a non-None package, but no __loader___
+    doctest.testfile(txtfile, package=pkgname)
+    doctest.master = None
+    
+    # Now try a package with a __loader___.get_data method
+    hook = InstallHook(hookpkgname)
+    doctest.testfile(txtfile, package=hookpkgname)
+    hook.remove()
+    del hook
+    doctest.master = None
+    
+    # Now try loading with module_relative=False
+    doctest.testfile(os.path.join(curdir, txtfile), module_relative=False)
+
+if __name__ == '__main__':
+    run()
Index: Lib/test/doctest_testfile.txt
===================================================================
--- Lib/test/doctest_testfile.txt	(revision 0)
+++ Lib/test/doctest_testfile.txt	(revision 0)
@@ -0,0 +1,11 @@
+This doctest verifies universal newline support; each command
+line has a different platform's end of line convention.
+
+(NOTE: Editing this file with a text editor could clobber the
+end of line characters!)
+
+  >>> print("Unix newline OK.")
+  Unix newline OK.
+  >>> print("Windows newline OK.")
+  Windows newline OK.
+  >>> print("MAC newline OK.")
  MAC newline OK.
\ No newline at end of file