diff --git a/plover_machine_hid.py b/plover_machine_hid.py
index 64b9c95..8d6ffec 100644
--- a/plover_machine_hid.py
+++ b/plover_machine_hid.py
@@ -43,7 +43,7 @@ SIMPLE_REPORT_LEN: int = 32
 class InvalidReport(Exception):
     pass
 
-STENO_KEY_CHART = set(f"X{i}" for i in range(1, N_LEVERS + 1))
+STENO_KEY_CHART = tuple(f"X{i}" for i in range(1, N_LEVERS + 1))
 
 print('steno key chart', len(STENO_KEY_CHART))
 class HidMachine(ThreadedStenotypeBase):