Index: Objects/unicodeobject.c
===================================================================
--- Objects/unicodeobject.c	(revision 62567)
+++ Objects/unicodeobject.c	(working copy)
@@ -3075,6 +3075,11 @@
 	    (*s != 'u' && *s != 'U')) {
 	    continue;
 	}
+        
+        if (PyErr_WarnPy3k("In 3.x raw strings, '\\U' and '\\u' escapes are "
+            "not treated specially.", 1) < 0)
+            goto onError;
+        
 	p--;
         count = *s=='u' ? 4 : 8;
 	s++;
Index: Lib/test/test_py3kwarn.py
===================================================================
--- Lib/test/test_py3kwarn.py	(revision 62567)
+++ Lib/test/test_py3kwarn.py	(working copy)
@@ -123,6 +123,13 @@
         with catch_warning() as w:
             self.assertWarning(buffer('a'), w, expected)
 
+    def test_raw_unicode_escape(self):
+        expected = "In 3.x raw strings, '\U' and '\u' escapes are " \
+            "not treated specially."
+        ur"\u1234"
+        with catch_warning() as w:
+            exec 'ur"\u1234"'
+            self.assertWarning(None, w, expected)
 
 def test_main():
     run_unittest(TestPy3KWarnings)