diff --git a/lib/tfw/fsm_base.py b/lib/tfw/fsm_base.py
index b7f270d..28b5ef6 100644
--- a/lib/tfw/fsm_base.py
+++ b/lib/tfw/fsm_base.py
@@ -52,10 +52,10 @@ class FSMBase(Machine, CallbackMixin):
         ]
 
     def step(self, trigger):
-        predicate_results = [
+        predicate_results = (
             predicate()
             for predicate in self.trigger_predicates[trigger]
-        ]
+        )
 
         # TODO: think about what could we do when this prevents triggering
         if all(predicate_results):