diff --git a/pytential/qbx/fmm.py b/pytential/qbx/fmm.py
index 4779a6000..6be86a262 100644
--- a/pytential/qbx/fmm.py
+++ b/pytential/qbx/fmm.py
@@ -400,8 +400,7 @@ def make_container():
 
 # {{{ FMM top-level
 
-def drive_fmm(expansion_wrangler, src_weight_vecs, timing_data=None,
-        traversal=None):
+def drive_fmm(expansion_wrangler, src_weight_vecs, timing_data=None):
     """Top-level driver routine for the QBX fast multipole calculation.
 
     :arg geo_data: A :class:`pytential.qbx.geometry.QBXFMMGeometryData` instance.
diff --git a/test/test_cost_model.py b/test/test_cost_model.py
index 2486227a7..9ca455d54 100644
--- a/test/test_cost_model.py
+++ b/test/test_cost_model.py
@@ -745,8 +745,8 @@ def test_cost_model_correctness(actx_factory, dim, off_surface,
     src_weights = np.ones(ndofs)
 
     timing_data = {}
-    potential = drive_fmm(wrangler, (src_weights,), timing_data,
-            traversal=wrangler.trav)[0][geo_data.ncenters:]
+    potential = drive_fmm(wrangler, (src_weights,), timing_data
+            )[0][geo_data.ncenters:]
 
     # Check constant one wrangler for correctness.
     assert np.all(potential == ndofs)