diff -r 8b1ac1a3d007 Doc/library/re.rst
--- a/Doc/library/re.rst	Wed Oct 08 22:32:50 2014 +0300
+++ b/Doc/library/re.rst	Thu Oct 09 11:45:02 2014 +0300
@@ -234,6 +234,9 @@ The special characters are:
    If there are non-whitespace characters before the flag, the results are
    undefined.
 
+   .. deprecated-removed:: 3.5 3.7
+      Flags should not be used in nested subexpression.
+
 ``(?:...)``
    A non-capturing version of regular parentheses.  Matches whatever regular
    expression is inside the parentheses, but the substring matched by the group
diff -r 8b1ac1a3d007 Lib/sre_parse.py
--- a/Lib/sre_parse.py	Wed Oct 08 22:32:50 2014 +0300
+++ b/Lib/sre_parse.py	Thu Oct 09 11:45:02 2014 +0300
@@ -377,7 +377,7 @@ def _parse_sub(source, state, nested=1):
     itemsappend = items.append
     sourcematch = source.match
     while 1:
-        itemsappend(_parse(source, state))
+        itemsappend(_parse(source, state, nested))
         if sourcematch("|"):
             continue
         if not nested:
@@ -430,9 +430,9 @@ def _parse_sub(source, state, nested=1):
     return subpattern
 
 def _parse_sub_cond(source, state, condgroup):
-    item_yes = _parse(source, state)
+    item_yes = _parse(source, state, 1)
     if source.match("|"):
-        item_no = _parse(source, state)
+        item_no = _parse(source, state, 1)
         if source.match("|"):
             raise error("conditional backref with more than two branches")
     else:
@@ -448,7 +448,7 @@ def _parse_sub_cond(source, state, condg
 _LOOKBEHINDASSERTCHARS = set("=!")
 _REPEATCODES = set([MIN_REPEAT, MAX_REPEAT])
 
-def _parse(source, state):
+def _parse(source, state, nested):
     # parse a simple pattern
     subpattern = SubPattern(state)
 
@@ -707,6 +707,11 @@ def _parse(source, state):
                             raise error("the group number is too large")
                 else:
                     # flags
+                    if nested:
+                        import warnings
+                        warnings.warn('Flags in nested suppattern. '
+                                      'Will be error in 3.7',
+                                      DeprecationWarning, stacklevel=7)
                     if not source.next in FLAGS:
                         raise error("unexpected end of pattern")
                     while source.next in FLAGS:
diff -r 8b1ac1a3d007 Lib/test/test_re.py
--- a/Lib/test/test_re.py	Wed Oct 08 22:32:50 2014 +0300
+++ b/Lib/test/test_re.py	Thu Oct 09 11:45:02 2014 +0300
@@ -1001,6 +1001,16 @@ class ReTests(unittest.TestCase):
         q = p.match(upper_char)
         self.assertTrue(q)
 
+    def test_nested_inline_flags(self):
+        with self.assertWarns(DeprecationWarning):
+            p = re.compile('(?:(?i))')
+        with self.assertWarns(DeprecationWarning):
+            p = re.compile('()(?(1)(?i))')
+        with self.assertWarns(DeprecationWarning):
+            p = re.compile('()(?(1)|(?i))')
+        with self.assertWarns(DeprecationWarning):
+            p = re.compile('(?=(?i))')
+
     def test_dollar_matches_twice(self):
         "$ matches the end of string, and just before the terminating \n"
         pattern = re.compile('$')