diff --git a/argos/commands.py b/argos/commands.py
index 746885b..e9b0f34 100644
--- a/argos/commands.py
+++ b/argos/commands.py
@@ -34,7 +34,9 @@ def coroutine(f):
 
 
 def validate_config_access(ctx, param, value):
-    for file in set(value, "argos-config.yaml", "/etc/argos/config.yaml"):
+    for file in list(
+        dict.fromkeys([value, "argos-config.yaml", "/etc/argos/config.yaml"])
+    ):
         path = Path(file)
 
         if path.is_file() and os.access(path, os.R_OK):