diff --git a/python/dune/perftool/blockstructured/vectorization.py b/python/dune/perftool/blockstructured/vectorization.py
index 0d7fb00c34da57d58f76e4928e2bc00b716fc18f..f8caeef4e562bd7550aee96c51ca86b38e5a9b53 100644
--- a/python/dune/perftool/blockstructured/vectorization.py
+++ b/python/dune/perftool/blockstructured/vectorization.py
@@ -157,8 +157,8 @@ def add_vcl_accum_insns(knl, iname_inner, iname_outer):
             new_insns.append(lp.Assignment(assignee=assignee_tail,
                                            expression=expr_tail,
                                            id=id_accum_tail,
-                                           depends_on=frozenset({id_accum, id_permute, id_set_left, id_init_a}) |
-                                                      frozenset(write_to_tail_ids),
+                                           depends_on=(frozenset({id_accum, id_permute, id_set_left, id_init_a}) |
+                                                       frozenset(write_to_tail_ids)),
                                            within_inames=(insn.within_inames - frozenset({iname_inner, iname_outer}) -
                                                           inames_micro) | inames_tail,
                                            tags=frozenset({'tail'})))
@@ -251,8 +251,8 @@ def add_vcl_access(knl, iname_inner):
         call_store = prim.Call(VCLStore(name_vec), (prim.Sum((prim.Variable(name_alias), index)),))
         store_insns.append(lp.CallInstruction(assignees=(), expression=call_store,
                                               id=store_id, within_inames=insn.within_inames,
-                                              depends_on=insn.depends_on | frozenset({id}) | read_dependencies[id] |
-                                                         write_ids))
+                                              depends_on=(insn.depends_on | frozenset({id}) | read_dependencies[id] |
+                                                          write_ids)))
 
     # replace alias with vcl vector, except for accumulation assignee
     vector_alias = [a for a in knl.arg_dict if a.endswith('alias')]
@@ -311,11 +311,11 @@ def add_vcl_access(knl, iname_inner):
                     from dune.perftool.error import PerftoolVectorizationError
                     raise PerftoolVectorizationError
                 new_insns.append(insn.copy(assignee=assignee_vec,
-                                           depends_on=insn.depends_on | read_dependencies[insn.id] |
-                                                      write_ids))
+                                           depends_on=(insn.depends_on | read_dependencies[insn.id] |
+                                                       write_ids)))
             else:
-                new_insns.append(insn.copy(depends_on=insn.depends_on | read_dependencies[insn.id] |
-                                                      write_ids))
+                new_insns.append(insn.copy(depends_on=(insn.depends_on | read_dependencies[insn.id] |
+                                                       write_ids)))
 
     return knl.copy(instructions=new_insns + load_insns + store_insns)