diff --git a/messaging/__init__.py b/messaging/__init__.py
index 5767521..b09db30 100644
--- a/messaging/__init__.py
+++ b/messaging/__init__.py
@@ -187,7 +187,7 @@ class SubMaster:
       except capnp.lib.capnp.KjException:  # pylint: disable=c-extension-no-member
         data = new_message(s, 0) # lists
 
-      self.data[s] = getattr(data, s)
+      self.data[s] = getattr(data.as_reader(), s)
       self.logMonoTime[s] = 0
       self.valid[s] = data.valid