diff --git a/intake_metabase/source.py b/intake_metabase/source.py
index 45753eb..bf24104 100644
--- a/intake_metabase/source.py
+++ b/intake_metabase/source.py
@@ -214,7 +214,7 @@ def get_databases(self):
         self._create_or_refresh_token()
 
         headers = _merge_dicts({'X-Metabase-Session': self._token}, self.extra_headers)
-        params = {'include': 'tables', 'saved': True}
+        params = json.dumps({'include': 'tables', 'saved': True})
 
         res = requests.get(
             urljoin(self.domain, '/api/database'),