diff -r 725131a5f6cf Lib/doctest.py
--- a/Lib/doctest.py	Sat Jul 04 22:52:33 2015 -0500
+++ b/Lib/doctest.py	Tue Jul 28 21:23:09 2015 -0400
@@ -1680,7 +1680,6 @@
             else:
                 assert 0, 'Bad diff option'
             # Remove trailing whitespace on diff output.
-            diff = [line.rstrip() + '\n' for line in diff]
             return 'Differences (%s):\n' % kind + _indent(''.join(diff))
 
         # If we're not using diff, then simply list the expected
diff -r 725131a5f6cf Lib/test/test_doctest.py
--- a/Lib/test/test_doctest.py	Sat Jul 04 22:52:33 2015 -0500
+++ b/Lib/test/test_doctest.py	Tue Jul 28 21:23:09 2015 -0400
@@ -1392,6 +1392,36 @@
           g
     TestResults(failed=1, attempted=1)
 
+The fancy reports had a bug for a long time where any trailing whitespace on
+the reported diff lines was stripped, making it impossible to see the
+differences in line reported as different that differed only in the amount of
+trailing whitespace.  The whitespace still isn't particularly visible unless
+you use NDIFF, but at least it is now there to be found.
+
+    >>> def f(x):
+    ...     r'''
+    ...     >>> print('\n'.join(['a    ', 'b']))
+    ...     a
+    ...     b
+    ...     '''
+
+    >>> test = doctest.DocTestFinder().find(f)[0]
+    >>> flags = doctest.REPORT_UDIFF
+    >>> doctest.DocTestRunner(verbose=False, optionflags=flags).run(test)
+    ... # doctest: +ELLIPSIS
+    **********************************************************************
+    File ..., line 3, in f
+    Failed example:
+        print('\n'.join(['a    ', 'b']))
+    Differences (context diff with expected followed by actual):
+        @@ -1,7 +1,7 @@
+        -a
+        +a    
+        b
+    TestResults(failed=1, attempted=1)
+
+NOTE: there is significant trailing whitespace on the +a line above;
+*DO NOT STRIP IT* when editing this file.
 
 The REPORT_NDIFF flag causes failures to use the difflib.Differ algorithm
 used by the popular ndiff.py utility.  This does intraline difference