diff --git a/dbt/adapters/factory.py b/dbt/adapters/factory.py
index e222cb24..be68357a 100644
--- a/dbt/adapters/factory.py
+++ b/dbt/adapters/factory.py
@@ -198,7 +198,11 @@ def get_adapter_constraint_support(self, name: Optional[str]) -> List[str]:
 FACTORY: AdapterContainer = AdapterContainer()
 
 
-def register_adapter(config: AdapterRequiredConfig, mp_context: SpawnContext, AdapterRegistered_log_level: EventLevel) -> None:
+def register_adapter(
+        config: AdapterRequiredConfig,
+        mp_context: SpawnContext,
+        AdapterRegistered_log_level: Optional[EventLevel] = EventLevel.INFO
+) -> None:
     FACTORY.register_adapter(config, mp_context, AdapterRegistered_log_level)