diff --git a/commpy/channelcoding/convcode.py b/commpy/channelcoding/convcode.py
index f26d310..9147a0a 100644
--- a/commpy/channelcoding/convcode.py
+++ b/commpy/channelcoding/convcode.py
@@ -257,7 +257,7 @@ def visualize(self, trellis_length = 2, state_order = None,
             edge_colors = ["#9E1BE0", "#06D65D"]
 
         if state_order is None:
-            state_order = range(self.number_states)
+            state_order = list(range(self.number_states))
 
         font = "sans-serif"
         fig = plt.figure()