diff --git a/volatility3/framework/plugins/windows/callbacks.py b/volatility3/framework/plugins/windows/callbacks.py
index 98e09d925..a1283d394 100644
--- a/volatility3/framework/plugins/windows/callbacks.py
+++ b/volatility3/framework/plugins/windows/callbacks.py
@@ -203,7 +203,7 @@ class Callbacks(interfaces.plugins.PluginInterface):
 
         callback_list = ntkrnlmp.object(object_type="_LIST_ENTRY", offset=symbol_offset)
         for callback in callback_list.to_list(full_type_name, "Link"):
-            altitude = "-"
+            altitude = None
             with contextlib.suppress(exceptions.InvalidAddressException):
                 altitude = callback.Altitude.String
             yield "CmRegisterCallbackEx", callback.Function, f"Altitude: {altitude}"