diff --git a/src/siglent_sdg/siglent.py b/src/siglent_sdg/siglent.py
index c8a4153..3523167 100644
--- a/src/siglent_sdg/siglent.py
+++ b/src/siglent_sdg/siglent.py
@@ -62,7 +62,7 @@ class Channel:
 class GenChannels:
     def __init__(self, instr: Resource):
         self.instr = instr
-        self.channels = {
+        self.channels: dict[ChannelID, Channel] = {
             ChannelID.CH1: Channel(ChannelID.CH1, instr),
             ChannelID.CH2: Channel(ChannelID.CH2, instr),
         }