diff -r 4fee906b9e9e Lib/sre_parse.py
--- a/Lib/sre_parse.py	Mon Jul 06 19:58:11 2015 +0300
+++ b/Lib/sre_parse.py	Tue Jul 07 12:36:59 2015 +0300
@@ -637,6 +637,10 @@ def _parse(source, state):
                         if gid is None:
                             msg = "unknown group name: {0!r}".format(name)
                             raise error(msg)
+                        if not state.checkgroup(gid):
+                            import warnings
+                            warnings.warn("symbolic reference to an open group",
+                                          RuntimeWarning)
                         if state.lookbehind:
                             import warnings
                             warnings.warn('group references in lookbehind '
diff -r 4fee906b9e9e Lib/test/test_re.py
--- a/Lib/test/test_re.py	Mon Jul 06 19:58:11 2015 +0300
+++ b/Lib/test/test_re.py	Tue Jul 07 12:36:59 2015 +0300
@@ -195,6 +195,7 @@ class ReTests(unittest.TestCase):
         re.compile('(?P<a>x)(?P=a)(?(a)y)')
         re.compile('(?P<a1>x)(?P=a1)(?(a1)y)')
         self.assertRaises(re.error, re.compile, '(?P<a>)(?P<a>)')
+        self.assertWarns(RuntimeWarning, re.compile, '(?P<a>(?P=a))')
         self.assertRaises(re.error, re.compile, '(?Px)')
         self.assertRaises(re.error, re.compile, '(?P=)')
         self.assertRaises(re.error, re.compile, '(?P=1)')