diff --git a/smile_base/models/base.py b/smile_base/models/base.py
index c65d137c..3dd107ae 100644
--- a/smile_base/models/base.py
+++ b/smile_base/models/base.py
@@ -207,6 +207,7 @@ def _read_group_process_groupby(self, gb, query):
                 'type': field_type,
                 'display_format': display_formats[gb_function or 'month'],
                 'interval': time_intervals[gb_function or 'month'],
+                'granularity': gb_function or 'month',
                 'tz_convert': tz_convert,
                 'qualified_field': qualified_field,
             }