diff --git a/fsl/wrappers/bet.py b/fsl/wrappers/bet.py
index a1405eb59fcef70c45a3a1600bd97c8bfe715670..09282f117b26374ab99a40420976fa0c1771dc8d 100644
--- a/fsl/wrappers/bet.py
+++ b/fsl/wrappers/bet.py
@@ -14,7 +14,7 @@ import fsl.utils.assertions as asrt
 from . import wrapperutils  as wutils
 
 
-@wutils.fileOrImage('input', 'output', outprefix='output')
+@wutils.fileOrImage('input', outprefix='output')
 @wutils.fslwrapper
 def bet(input, output, **kwargs):
     """Wrapper for the ``bet`` command.