diff --git a/pypeflow/do_task.py b/pypeflow/do_task.py
index 03235d9..ea210f0 100644
--- a/pypeflow/do_task.py
+++ b/pypeflow/do_task.py
@@ -142,7 +142,7 @@ def __getattr__(self, name):
             result = self.kwds.itervalues()
         else:
             result = [str(self.kwds[name])]
-        return ' '.join(self.quote(v) for v in result)
+        return ' '.join(self.quote(v) for v in sorted(result))
     def __init__(self, kwds, quote=quote):
         self.kwds = kwds
         self.quote = quote
diff --git a/test/test_do_task.py b/test/test_do_task.py
index 80a833d..e082bf7 100644
--- a/test/test_do_task.py
+++ b/test/test_do_task.py
@@ -35,7 +35,7 @@
 echo PP
 """),
         # input.i* (with quoting)
-        ({'ii': 'II', 'ij': 'I J', 'ab': 'AB'}, {'oo': 'OO'}, {'pp': 'PP'},
+        ({'ii': 'II', 'ij': 'I J', 'ia': 'IA', 'ab': 'AB'}, {'oo': 'OO'}, {'pp': 'PP'},
 """\
 echo {input.i*}
 echo {input.ab}
@@ -43,7 +43,7 @@
 echo {params.pp}
 """,
 """\
-echo II 'I J'
+echo 'I J' IA II
 echo AB
 echo OO
 echo PP