diff --git a/pytools/obj_array.py b/pytools/obj_array.py
index f4a74e0aa2b43505d643fcfc7c880a2df5a1e258..6dfd52bbba78f80dfe0e0919a317cc9ea7004bd7 100644
--- a/pytools/obj_array.py
+++ b/pytools/obj_array.py
@@ -85,7 +85,7 @@ def join_fields(*args):
             if log_shape(arg) == ():
                 res_list.append(arg)
             else:
-                res_list.extend(arg)
+                res_list.extend(arg.flat)
         else:
             res_list.append(arg)