diff --git a/fsl/wrappers/wrapperutils.py b/fsl/wrappers/wrapperutils.py
index bac9cc33c2129f8ce78519ae9676bdf2b5f9e8e8..a2ec6eb50590dad84a5b59b1019cd02adae56afc 100644
--- a/fsl/wrappers/wrapperutils.py
+++ b/fsl/wrappers/wrapperutils.py
@@ -558,8 +558,8 @@ class _FileOrThing(object):
         allargs  = {k : v for k, v in zip(argnames, args)}
         allargs.update(kwargs)
 
-        if len(self.__things) == 0: things = self.__things
-        else:                       things = allargs.keys()
+        if len(self.__things) > 0: things = self.__things
+        else:                      things = allargs.keys()
 
         for name in things: