diff --git a/superset/views/core.py b/superset/views/core.py
index 2b6924db8c3..48a5e8ee7c6 100755
--- a/superset/views/core.py
+++ b/superset/views/core.py
@@ -2252,6 +2252,8 @@ class Superset(BaseSupersetView):
             try:
                 dtype = '{}'.format(col['type'])
             except Exception:
+                # sqla.types.JSON __str__ has a bug, so using __class__.
+                dtype = col['type'].__class__.__name__
                 pass
             payload_columns.append({
                 'name': col['name'],