diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 4143681..b76f373 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -539,11 +539,15 @@
 	PyCompilerFlags cf;
 	int exists;
 
-	if (!PyArg_ParseTuple(args, "s|O!O!:execfile",
+	if (!PyArg_ParseTuple(args, "s|O!O:execfile",
 			&filename,
 			&PyDict_Type, &globals,
-			&PyDict_Type, &locals))
+			&locals))
 		return NULL;
+	if (locals != Py_None && !PyMapping_Check(locals)) {
+		PyErr_SetString(PyExc_TypeError, "locals must be a mapping");
+		return NULL;
+	}
 	if (globals == Py_None) {
 		globals = PyEval_GetGlobals();
 		if (locals == Py_None)
diff --git a/Python/ceval.c b/Python/ceval.c
index 152b942..3a462af 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1643,7 +1643,7 @@
 			w = GETITEM(names, oparg);
 			v = POP();
 			if ((x = f->f_locals) != NULL) {
-				if (PyDict_CheckExact(v))
+				if (PyDict_CheckExact(x))
 					err = PyDict_SetItem(x, w, v);
 				else
 					err = PyObject_SetItem(x, w, v);
@@ -4116,9 +4116,9 @@
 		    "exec: arg 2 must be a dictionary or None");
 		return -1;
 	}
-	if (!PyDict_Check(locals)) {
+	if (!PyMapping_Check(locals)) {
 		PyErr_SetString(PyExc_TypeError,
-		    "exec: arg 3 must be a dictionary or None");
+		    "exec: arg 3 must be a mapping or None");
 		return -1;
 	}
 	if (PyDict_GetItemString(globals, "__builtins__") == NULL)