diff --git a/tiramisu/function.py b/tiramisu/function.py
index 8630eb4..b531d1d 100644
--- a/tiramisu/function.py
+++ b/tiramisu/function.py
@@ -19,14 +19,14 @@ class Params:
     __slots__ = ('args', 'kwargs')
     def __init__(self, args=None, kwargs=None):
         if args is None:
-            args = tuple()
+            args = []
         if kwargs is None:
             kwargs = {}
         if isinstance(args, Param):
             args = (args,)
         else:
-            if not isinstance(args, tuple):
-                raise ValueError(_('args in params must be a tuple'))
+            if not isinstance(args, list):
+                raise ValueError(_('args in params must be a list'))
             for arg in args:
                 if not isinstance(arg, Param):
                     raise ValueError(_('arg in params must be a Param'))