diff --git a/bijoe/engine.py b/bijoe/engine.py
index b44bd8c..3a4d862 100644
--- a/bijoe/engine.py
+++ b/bijoe/engine.py
@@ -259,8 +259,13 @@ class EngineCube(object):
             json_key = name[5:]
             return schemas.Join(
                 name=name,
-                table='(SELECT DISTINCT %s.%s->>\'%s\' AS value FROM %s ORDER BY value)' % (
-                    self.fact_table, self.json_field, json_key, self.fact_table),
+                table=(
+                    '(SELECT DISTINCT %s.%s->>\'%s\' AS value FROM %s '
+                    'WHERE %s.%s->>\'%s\' IS NOT NULL ORDER BY value)' % (
+                        self.fact_table, self.json_field, json_key, self.fact_table,
+                        self.fact_table, self.json_field, json_key
+                    )
+                ),
                 master='%s->>\'%s\'' % (self.json_field, json_key),
                 detail='value',
             )