diff --git a/src/stpipe/container.py b/src/stpipe/container.py
index 562dce5b..92852015 100644
--- a/src/stpipe/container.py
+++ b/src/stpipe/container.py
@@ -39,7 +39,7 @@ def __subclasshook__(cls, C):
         save_signature = inspect.signature(C.save)
         target_signature = inspect.signature(cls.save)
         for parameter in target_signature.parameters:
-            if parameter == 'self':
+            if parameter == "self":
                 pass
             # check that this parameter/argument exists in the save function
             if parameter not in save_signature.parameters: