diff --git a/boxtree/fmm.py b/boxtree/fmm.py
index ba7dbcc7836ce3211c0b10d0bf64a5c1bc73064e..eca9e3e80662102bc919702c1ae6da299cc6fcc8 100644
--- a/boxtree/fmm.py
+++ b/boxtree/fmm.py
@@ -76,7 +76,7 @@ def drive_fmm(traversal, expansion_wrangler, src_weights):
         start_parent_box, end_parent_box = \
                 traversal.level_start_source_parent_box_nrs[lev:lev+2]
         wrangler.coarsen_multipoles(
-                traversal.source_parent_boxes, start_parent_box, end_parent_box,
+                traversal.source_parent_boxes[start_parent_box:end_parent_box],
                 mpole_exps)
 
     # mpole_exps is called Phi in [1]
@@ -168,8 +168,8 @@ def drive_fmm(traversal, expansion_wrangler, src_weights):
         start_box, end_box = \
                 traversal.level_start_target_or_target_parent_box_nrs[lev:lev+2]
         wrangler.refine_locals(
-                traversal.target_or_target_parent_boxes,
-                start_box, end_box, local_exps)
+                traversal.target_or_target_parent_boxes[start_box:end_box],
+                local_exps)
 
     # }}}
 
@@ -244,9 +244,8 @@ class ExpansionWranglerInterface:
         All other expansions must be zero.
         """
 
-    def coarsen_multipoles(self, parent_boxes, start_parent_box, end_parent_box,
-            mpoles):
-        """For each box in ``parent_boxes[start_parent_box:end_parent_box]``,
+    def coarsen_multipoles(self, parent_boxes, mpoles):
+        """For each box in *parent_boxes*,
         gather (and translate) the box's children's multipole expansions in
         *mpole* and add the resulting expansion into the box's multipole
         expansion in *mpole*.
@@ -295,8 +294,8 @@ class ExpansionWranglerInterface:
         """
         pass
 
-    def refine_locals(self, child_boxes, start_child_box, end_child_box, local_exps):
-        """For each box in *child_boxes[start_child_box:end_child_box]*,
+    def refine_locals(self, child_boxes, local_exps):
+        """For each box in *child_boxes*,
         translate the box's parent's local expansion in *local_exps* and add
         the resulting expansion into the box's local expansion in *local_exps*.
 
diff --git a/boxtree/pyfmmlib_integration.py b/boxtree/pyfmmlib_integration.py
index 0942a9690e03a8b1aa4b054c593dce7e88d3fc9d..86c57ad29da6f1769b18a49fdc7bd9d998d8b517 100644
--- a/boxtree/pyfmmlib_integration.py
+++ b/boxtree/pyfmmlib_integration.py
@@ -102,14 +102,13 @@ class Helmholtz2DExpansionWrangler:
 
         return mpoles
 
-    def coarsen_multipoles(self, parent_boxes, start_parent_box, end_parent_box,
-            mpoles):
+    def coarsen_multipoles(self, parent_boxes, mpoles):
         tree = self.tree
         rscale = 1  # FIXME
 
         from pyfmmlib import h2dmpmp_vec
 
-        for ibox in parent_boxes[start_parent_box:end_parent_box]:
+        for ibox in parent_boxes:
             parent_center = tree.box_centers[:, ibox]
             for child in tree.box_child_ids[:, ibox]:
                 if child:
@@ -241,12 +240,12 @@ class Helmholtz2DExpansionWrangler:
 
         return local_exps
 
-    def refine_locals(self, child_boxes, start_child_box, end_child_box, local_exps):
+    def refine_locals(self, child_boxes, local_exps):
         rscale = 1  # FIXME
 
         from pyfmmlib import h2dlocloc_vec
 
-        for tgt_ibox in child_boxes[start_child_box:end_child_box]:
+        for tgt_ibox in child_boxes:
             tgt_center = self.tree.box_centers[:, tgt_ibox]
             src_ibox = self.tree.box_parent_ids[tgt_ibox]
             src_center = self.tree.box_centers[:, src_ibox]
diff --git a/test/test_fmm.py b/test/test_fmm.py
index 66899bfee3f86e3ce3e8a3f516ff81183f06e707..09ef5ebfbfabe4e8c124cb379fd3b81f146d2525 100644
--- a/test/test_fmm.py
+++ b/test/test_fmm.py
@@ -84,11 +84,10 @@ class ConstantOneExpansionWrangler:
 
         return mpoles
 
-    def coarsen_multipoles(self, parent_boxes, start_parent_box, end_parent_box,
-            mpoles):
+    def coarsen_multipoles(self, parent_boxes, mpoles):
         tree = self.tree
 
-        for ibox in parent_boxes[start_parent_box:end_parent_box]:
+        for ibox in parent_boxes:
             for child in tree.box_child_ids[:, ibox]:
                 if child:
                     mpoles[ibox] += mpoles[child]
@@ -161,8 +160,8 @@ class ConstantOneExpansionWrangler:
 
         return local_exps
 
-    def refine_locals(self, child_boxes, start_child_box, end_child_box, local_exps):
-        for ibox in child_boxes[start_child_box:end_child_box]:
+    def refine_locals(self, child_boxes, local_exps):
+        for ibox in child_boxes:
             local_exps[ibox] += local_exps[self.tree.box_parent_ids[ibox]]
 
         return local_exps