diff --git a/python/dune/perftool/sumfact/realization.py b/python/dune/perftool/sumfact/realization.py
index 6d99175e753d126f9f73a61138616abe79f11352..bc24f488d3ce8e961b292d9014c1f4a9cdfa7ee8 100644
--- a/python/dune/perftool/sumfact/realization.py
+++ b/python/dune/perftool/sumfact/realization.py
@@ -68,6 +68,11 @@ def _realize_input(sf, insn_dep):
                    context_tags=("kernel",),
                    cache_key_generator=lambda s, **kw: s.cache_key)
 def _realize_sum_factorization_kernel(sf, insn_dep=frozenset(), outshape=None, direct_input=None, direct_output=None):
+    # Unify the insn_dep parameter to be a frozenset
+    if isinstance(insn_dep, str):
+        insn_dep = frozenset({insn_dep})
+    assert isinstance(insn_dep, frozenset)
+
     # Get the vectorization info. During dry run, this is a now op
 #    sf = attach_vectorization_info(sf)
     if get_global_context_value("dry_run", False):