diff --git a/Python/ast.c b/Python/ast.c
index 27c3efa..42dcc2d 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -1869,6 +1869,10 @@
                     return NULL;
                 }
                 key = e->v.Name.id;
+                if (!strcmp(PyString_AS_STRING(key), "None")) {
+                    ast_error(CHILD(ch, 0), "assignment to None");
+                    return NULL;
+                }
                 e = ast_for_expr(c, CHILD(ch, 2));
                 if (!e)
                     return NULL;