diff --git a/checker/synapse_grafana.py b/checker/synapse_grafana.py
index f62bd91..4cb822b 100644
--- a/checker/synapse_grafana.py
+++ b/checker/synapse_grafana.py
@@ -312,7 +312,7 @@ def get_waiting_for_db(api_key, interval, data_range, endpoint):
     response = requests.post(f'{endpoint}/api/ds/query', headers={'Authorization': f'Bearer {api_key}'}, json=json_data, verify=False).json()
     data = response['results']['A']['frames'][0]['data']['values'][1]
     null_present = False
-    for i in range(data):
+    for i in range(len(data)):
         if data[i] is None:
             data[i] = -1
             null_present = True