diff --git a/aliby/io/image.py b/aliby/io/image.py
index 32e0a3822305fb4d16adac42da3100371a23dc4e..83571b3ecb3bf238e6fac4ee2aca7da23d604385 100644
--- a/aliby/io/image.py
+++ b/aliby/io/image.py
@@ -39,7 +39,7 @@ class ImageLocal:
             # Mark non-existent dimensions for padding
             base = "TCZXY"
             self.base = base
-            self.ids = {base.index(i) for i in dimorder}
+            self.ids = [base.index(i) for i in dimorder]
 
             self._dimorder = dimorder