Index: Python/getargs.c
===================================================================
--- Python/getargs.c	(revision 80121)
+++ Python/getargs.c	(working copy)
@@ -1607,6 +1607,28 @@
 	return retval;
 }
 
+int
+PyArg_ValidateKeywordArguments(PyObject *kwargs)
+{
+	Py_ssize_t pos = 0;
+	PyObject *key, *value;
+	if (!PyDict_CheckExact(kwargs)) {
+		PyErr_BadInternalCall();
+		return 0;
+	}
+	/* Check if we can bypass looking through the whole dict. */
+	if (!_PyDict_Optimized(kwargs)) {
+		while (PyDict_Next(kwargs, &pos, &key, &value)) {
+			if (!(PyUnicode_Check(key))) {
+				PyErr_SetString(PyExc_TypeError,
+						"keyword arguments must be strings");
+				return 0;
+			}
+		}
+	}
+	return 1;
+}
+
 #define IS_END_OF_FORMAT(c) (c == '\0' || c == ';' || c == ':')
 
 static int
Index: Include/dictobject.h
===================================================================
--- Include/dictobject.h	(revision 80121)
+++ Include/dictobject.h	(working copy)
@@ -126,6 +126,7 @@
 PyAPI_FUNC(int) _PyDict_Contains(PyObject *mp, PyObject *key, long hash);
 PyAPI_FUNC(PyObject *) _PyDict_NewPresized(Py_ssize_t minused);
 PyAPI_FUNC(void) _PyDict_MaybeUntrack(PyObject *mp);
+PyAPI_FUNC(int) _PyDict_Optimized(PyObject *mp);
 
 /* PyDict_Update(mp, other) is equivalent to PyDict_Merge(mp, other, 1). */
 PyAPI_FUNC(int) PyDict_Update(PyObject *mp, PyObject *other);
Index: Include/modsupport.h
===================================================================
--- Include/modsupport.h	(revision 80121)
+++ Include/modsupport.h	(working copy)
@@ -27,6 +27,7 @@
 PyAPI_FUNC(int) PyArg_ParseTuple(PyObject *, const char *, ...) Py_FORMAT_PARSETUPLE(PyArg_ParseTuple, 2, 3);
 PyAPI_FUNC(int) PyArg_ParseTupleAndKeywords(PyObject *, PyObject *,
                                                   const char *, char **, ...);
+PyAPI_FUNC(int) PyArg_ValidateKeywordArguments(PyObject *);
 PyAPI_FUNC(int) PyArg_UnpackTuple(PyObject *, const char *, Py_ssize_t, Py_ssize_t, ...);
 PyAPI_FUNC(PyObject *) Py_BuildValue(const char *, ...);
 PyAPI_FUNC(PyObject *) _Py_BuildValue_SizeT(const char *, ...);
Index: Objects/dictobject.c
===================================================================
--- Objects/dictobject.c	(revision 80121)
+++ Objects/dictobject.c	(working copy)
@@ -458,6 +458,13 @@
 	return 0;
 }
 
+int
+_PyDict_Optimized(PyObject *dict)
+{
+	assert(PyDict_CheckExact(dict));
+	return ((PyDictObject *)dict)->ma_lookup == lookdict_unicode;
+}
+
 #ifdef SHOW_TRACK_COUNT
 #define INCREASE_TRACK_COUNT \
 	(count_tracked++, count_untracked--);
@@ -1386,8 +1393,12 @@
 		else
 			result = PyDict_MergeFromSeq2(self, arg, 1);
 	}
-	if (result == 0 && kwds != NULL)
-		result = PyDict_Merge(self, kwds, 1);
+	if (result == 0 && kwds != NULL) {
+		if (PyArg_ValidateKeywordArguments(kwds))
+			result = PyDict_Merge(self, kwds, 1);
+		else
+			result = -1;
+	}
 	return result;
 }
 
Index: Doc/c-api/arg.rst
===================================================================
--- Doc/c-api/arg.rst	(revision 80121)
+++ Doc/c-api/arg.rst	(working copy)
@@ -366,6 +366,13 @@
    va_list rather than a variable number of arguments.
 
 
+.. cfunction:: int PyArg_ValidateKeywordArguments(PyObject *)
+
+   Ensure that the keys in the keywords argument dictionary are strings.  This
+   is only needed if :cfunc:`PyArg_ParseTupleAndKeywords` is not used, since the
+   latter already does this check.
+
+
 .. XXX deprecated, will be removed
 .. cfunction:: int PyArg_Parse(PyObject *args, const char *format, ...)
 
Index: Lib/test/test_dict.py
===================================================================
--- Lib/test/test_dict.py	(revision 80121)
+++ Lib/test/test_dict.py	(working copy)
@@ -7,6 +7,12 @@
 
 class DictTest(unittest.TestCase):
 
+    def test_invalid_keyword_arguments(self):
+        with self.assertRaises(TypeError):
+            dict(**{1 : 2})
+        with self.assertRaises(TypeError):
+            {}.update(**{1 : 2})
+
     def test_constructor(self):
         # calling built-in types without argument must return empty
         self.assertEqual(dict(), {})