diff --git a/tmtc/acs_subsystem.py b/tmtc/acs_subsystem.py
index 80bc85a..650a1f7 100644
--- a/tmtc/acs_subsystem.py
+++ b/tmtc/acs_subsystem.py
@@ -64,7 +64,7 @@ def build_acs_subsystem_cmd(p: ServiceProviderParams):
                 app_data=ACS_SUBSYSTEM_ID,
             )
         )
-    mode_info_tup = HANDLER_LIST[op_code]
+    mode_info_tup = HANDLER_LIST.get(op_code)
     if mode_info_tup is None:
         return
     pack_mode_cmd_with_info(