diff --git a/companion.py b/companion.py
index 84f25209..1cd202bb 100644
--- a/companion.py
+++ b/companion.py
@@ -129,8 +129,7 @@ def listify(thing):
         return retval
 
     else:
-        assert False, thing  # we expect an array or a sparse array
-        return list(thing)  # hope for the best
+        raise ValueError("expected an array or sparse array")
 
 
 class ServerError(Exception):