diff --git a/aten/src/ATen/core/function_schema.h b/aten/src/ATen/core/function_schema.h
index ab021c69cf3..68e177a225d 100644
--- a/aten/src/ATen/core/function_schema.h
+++ b/aten/src/ATen/core/function_schema.h
@@ -406,7 +406,7 @@ inline std::ostream& operator<<(std::ostream& out, const Argument& arg) {
 
   if (arg.default_value()) {
     out << "=";
-    if (type->kind() == c10::TypeKind::StringType) {
+    if (type->kind() == c10::TypeKind::StringType || (unopt_type->kind() == c10::TypeKind::StringType && !arg.default_value().value().isNone())) {
       printQuotedString(out, arg.default_value().value().toStringRef());
     } else {
       out << arg.default_value().value();
diff --git a/test/test_function_schema.py b/test/test_function_schema.py
index 5a152737347..2f81c0bae76 100644
--- a/test/test_function_schema.py
+++ b/test/test_function_schema.py
@@ -86,5 +86,10 @@ class TestFunctionSchema(TestCase):
         new_schema = parse_schema('any(Tensor self, *, Tensor b, int[] c) -> Tensor')
         self.assertFalse(new_schema.is_backward_compatible_with(old_schema))
 
+    def test_string_optional_parameter_default_value(self):
+        schema_a = parse_schema("example::op(str? order=\"NCHW\") -> (Tensor)")
+        schema_b = parse_schema(str(schema_a))
+        self.assertEquals(schema_a, schema_b)
+
 if __name__ == '__main__':
     run_tests()