diff --git a/fsl/utils/filetree/query.py b/fsl/utils/filetree/query.py
index 10c86374d8971835134741669df7811efca31a50..70e1306f3bafeaac97e8798473a2f180badfa98f 100644
--- a/fsl/utils/filetree/query.py
+++ b/fsl/utils/filetree/query.py
@@ -132,10 +132,10 @@ class FileTreeQuery(object):
         files of that ``short_name`` type are returned.
         """
         if short_name is None:
-            return dict(self.__allvars)
+            return {var : list(vals) for var, vals in self.__allvars.items()}
         else:
             varnames = self.__shortnamevars[short_name]
-            return {var : self.__allvars[var] for var in varnames}
+            return {var : list(self.__allvars[var]) for var in varnames}
 
 
     @property