diff --git a/schema.py b/schema.py
index d3a583f..28f3b2f 100644
--- a/schema.py
+++ b/schema.py
@@ -306,7 +306,7 @@
     },
     "then": {
         "properties": system_settings_schema,
-        "required": system_settings_schema.keys()
+        "required": list(system_settings_schema.keys())
     },
     "else": {
         "properties": {