class objects are read-only in restricted mode
diff --git a/Objects/classobject.c b/Objects/classobject.c
index d4a873f..0d0a109 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -174,6 +174,11 @@
 			return -1;
 		}
 	}
+	if (getrestricted()) {
+		err_setstr(RuntimeError,
+			   "classes are read-only in restricted mode");
+		return -1;
+	}
 	ac = dictlookup(op->cl_dict, name);
 	if (ac != NULL && is_accessobject(ac))
 		return setaccessvalue(ac, getowner(), v);