diff -r 11cf18ec1900 Lib/sre_parse.py
--- a/Lib/sre_parse.py	Sat Sep 06 22:49:07 2014 +0300
+++ b/Lib/sre_parse.py	Mon Sep 08 14:02:50 2014 +0300
@@ -283,7 +283,12 @@
         elif c in OCTDIGITS:
             # octal escape (up to three digits)
             escape += source.getwhile(2, OCTDIGITS)
-            return LITERAL, int(escape[1:], 8) & 0xff
+            c = int(escape[1:], 8)
+            if c > 0o377:
+                import warnings
+                warnings.warn('octal escape value > 0o377',
+                              UserWarning, stacklevel=8)
+            return LITERAL, c & 0xff
         elif c in DIGITS:
             raise ValueError
         if len(escape) == 2:
@@ -325,7 +330,7 @@
         elif c == "0":
             # octal escape
             escape += source.getwhile(2, OCTDIGITS)
-            return LITERAL, int(escape[1:], 8) & 0xff
+            return LITERAL, int(escape[1:], 8)
         elif c in DIGITS:
             # octal escape *or* decimal group reference (sigh)
             if source.next in DIGITS:
@@ -334,7 +339,12 @@
                     source.next in OCTDIGITS):
                     # got three octal digits; this is an octal escape
                     escape = escape + source.get()
-                    return LITERAL, int(escape[1:], 8) & 0xff
+                    c = int(escape[1:], 8)
+                    if c > 0o377:
+                        import warnings
+                        warnings.warn('octal escape value > 0o377',
+                                      UserWarning, stacklevel=8)
+                    return LITERAL, c & 0xff
             # not an octal escape, so this is a group reference
             group = int(escape[1:])
             if group < state.groups:
@@ -825,7 +835,12 @@
                         s.next in OCTDIGITS):
                         this += sget()
                         isoctal = True
-                        lappend(chr(int(this[1:], 8) & 0xff))
+                        c = int(this[1:], 8)
+                        if c > 0o377:
+                            import warnings
+                            warnings.warn('octal escape value > 0o377',
+                                          UserWarning, stacklevel=4)
+                        lappend(chr(c & 0xff))
                 if not isoctal:
                     addgroup(int(this[1:]))
             else:
diff -r 11cf18ec1900 Lib/test/test_re.py
--- a/Lib/test/test_re.py	Sat Sep 06 22:49:07 2014 +0300
+++ b/Lib/test/test_re.py	Mon Sep 08 14:02:50 2014 +0300
@@ -154,8 +154,10 @@
         self.assertEqual(re.sub('x', r'\09', 'x'), '\0' + '9')
         self.assertEqual(re.sub('x', r'\0a', 'x'), '\0' + 'a')
 
-        self.assertEqual(re.sub('x', r'\400', 'x'), '\0')
-        self.assertEqual(re.sub('x', r'\777', 'x'), '\377')
+        with self.assertWarnsRegex(UserWarning, 'octal escape value > 0o377'):
+            self.assertEqual(re.sub('x', r'\400', 'x'), '\0')
+        with self.assertWarnsRegex(UserWarning, 'octal escape value > 0o377'):
+            self.assertEqual(re.sub('x', r'\777', 'x'), '\377')
 
         self.assertRaises(re.error, re.sub, 'x', r'\1', 'x')
         self.assertRaises(re.error, re.sub, 'x', r'\8', 'x')
@@ -691,7 +693,8 @@
         self.assertIsNotNone(re.match(r"\08", "\0008"))
         self.assertIsNotNone(re.match(r"\01", "\001"))
         self.assertIsNotNone(re.match(r"\018", "\0018"))
-        self.assertIsNotNone(re.match(r"\567", chr(0o167)))
+        with self.assertWarnsRegex(UserWarning, 'octal escape value > 0o377'):
+            self.assertIsNotNone(re.match(r"\567", chr(0o167)))
         self.assertRaises(re.error, re.match, r"\911", "")
         self.assertRaises(re.error, re.match, r"\x1", "")
         self.assertRaises(re.error, re.match, r"\x1z", "")
@@ -719,6 +722,8 @@
             self.assertIsNotNone(re.match(r"[\U%08x]" % i, chr(i)))
             self.assertIsNotNone(re.match(r"[\U%08x0]" % i, chr(i)+"0"))
             self.assertIsNotNone(re.match(r"[\U%08xz]" % i, chr(i)+"z"))
+        with self.assertWarnsRegex(UserWarning, 'octal escape value > 0o377'):
+            self.assertIsNotNone(re.match(r"[\567]", chr(0o167)))
         self.assertIsNotNone(re.match(r"[\U0001d49c-\U0001d4b5]", "\U0001d49e"))
         self.assertRaises(re.error, re.match, r"[\911]", "")
         self.assertRaises(re.error, re.match, r"[\x1z]", "")
@@ -740,7 +745,8 @@
         self.assertIsNotNone(re.match(br"\08", b"\0008"))
         self.assertIsNotNone(re.match(br"\01", b"\001"))
         self.assertIsNotNone(re.match(br"\018", b"\0018"))
-        self.assertIsNotNone(re.match(br"\567", bytes([0o167])))
+        with self.assertWarnsRegex(UserWarning, 'octal escape value > 0o377'):
+            self.assertIsNotNone(re.match(br"\567", bytes([0o167])))
         self.assertRaises(re.error, re.match, br"\911", b"")
         self.assertRaises(re.error, re.match, br"\x1", b"")
         self.assertRaises(re.error, re.match, br"\x1z", b"")
@@ -755,6 +761,8 @@
             self.assertIsNotNone(re.match((r"[\x%02x]" % i).encode(), bytes([i])))
             self.assertIsNotNone(re.match((r"[\x%02x0]" % i).encode(), bytes([i])))
             self.assertIsNotNone(re.match((r"[\x%02xz]" % i).encode(), bytes([i])))
+        with self.assertWarnsRegex(UserWarning, 'octal escape value > 0o377'):
+            self.assertIsNotNone(re.match(br"[\567]", bytes([0o167])))
         self.assertIsNotNone(re.match(br"[\u]", b'u'))
         self.assertIsNotNone(re.match(br"[\U]", b'U'))
         self.assertRaises(re.error, re.match, br"[\911]", "")