diff --git a/jsonfield/fields.py b/jsonfield/fields.py
index dd390ef..9ef5caf 100644
--- a/jsonfield/fields.py
+++ b/jsonfield/fields.py
@@ -97,7 +97,7 @@ class JSONField(models.Field):
         return json.dumps(value, **self.encoder_kwargs)
 
     def value_to_string(self, obj):
-        return self._get_val_from_obj(obj)
+        return self.value_from_object(obj)
 
 
 class NoPrepareMixin(object):