diff --git a/nb2kg/nb2kg/managers.py b/nb2kg/nb2kg/managers.py
index 105e0fc..404f957 100644
--- a/nb2kg/nb2kg/managers.py
+++ b/nb2kg/nb2kg/managers.py
@@ -241,6 +241,7 @@ def shutdown_all(self):
             try:
                 response = client.fetch(kernel_url, 
                     headers=KG_HEADERS,
+                    validate_cert=VALIDATE_KG_CERT,                    
                     method='DELETE'
                 )
             except HTTPError: