diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -2729,6 +2729,10 @@ class UnicodeTest(string_tests.CommonTest,
         support.check_free_after_iterating(self, iter, str)
         support.check_free_after_iterating(self, reversed, str)
 
+    def test_invalid_sequences(self):
+        for letter in "cdeghijklmopqswyzABCDEFGHIJKLMOPQRSTVWXYZ":
+            with self.assertWarns(DeprecationWarning):
+                eval(r"'\%s'" % letter)
 
 class StringModuleTest(unittest.TestCase):
     def test_formatter_parser(self):
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -5848,6 +5848,7 @@ PyUnicode_DecodeUnicodeEscape(const char *s,
     _PyUnicodeWriter writer;
     const char *end;
     char* message;
+    int ret;
     Py_UCS4 chr = 0xffffffff; /* in case 'getcode' messes up */
     PyObject *errorHandler = NULL;
     PyObject *exc = NULL;
@@ -6022,6 +6023,11 @@ PyUnicode_DecodeUnicodeEscape(const char *s,
                 goto error;
             }
             else {
+                /* Deprecate invalid escape sequences */
+                ret = PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
+                                       "invalid escape sequence '%c'", c);
+                if (ret < 0)
+                    goto onError;
                 WRITECHAR('\\');
                 WRITECHAR((unsigned char)s[-1]);
             }