diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 39a38ed0c038013551719f6194937cc8e7c6b632..1467e0c1cdc71a45465b96db3e1b44e50892216e 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -18,7 +18,7 @@ Python 3 Titan V:
     script:
     - export PY_EXE=python3
     - export PYOPENCL_TEST=nvi:titan
-    - EXTRA_INSTALL="pybind11 numpy mako"
+    - EXTRA_INSTALL="pybind11 numpy mako matplotlib"
     - curl -L -O -k https://gitlab.tiker.net/inducer/ci-support/raw/master/build-and-test-py-project.sh
     - ". ./build-and-test-py-project.sh"
     tags:
@@ -68,7 +68,7 @@ Python 3 POCL:
     script:
     - export PY_EXE=python3
     - export PYOPENCL_TEST=portable
-    - export EXTRA_INSTALL="pybind11 numpy mako"
+    - export EXTRA_INSTALL="pybind11 numpy mako matplotlib"
     - curl -L -O -k https://gitlab.tiker.net/inducer/ci-support/raw/master/build-and-test-py-project.sh
     - ". ./build-and-test-py-project.sh"
     tags:
diff --git a/boxtree/traversal.py b/boxtree/traversal.py
index 2d60f68725ea5f1b2b95a77f7b547f5954cd6951..e99b7d83b50f7d4fd7c34bf0cefb555974f5b3a4 100644
--- a/boxtree/traversal.py
+++ b/boxtree/traversal.py
@@ -1566,7 +1566,8 @@ class FMMTraversalInfo(DeviceDataRecord):
         type ``box_id_t``.  (Note: This list contains global box numbers, not
         indices into :attr:`source_boxes`.)
 
-        Note *starts* are indexed by `target_boxes_sep_smaller_by_source_level`. For
+        Note *starts* are indexed along with
+        `target_boxes_sep_smaller_by_source_level`. For
         example, for level *i*, *lists[starts[j]:starts[j+1]]* represents "List 3"
         source boxes of *target_boxes_sep_smaller_by_source_level[i][j]* on level
         *i*.
diff --git a/boxtree/visualization.py b/boxtree/visualization.py
index e5fb19de8fbfe51e6003a6f346bcfca076f890db..e9671e07deb961eb9cd3cd9bf53447d5dcf69a67 100644
--- a/boxtree/visualization.py
+++ b/boxtree/visualization.py
@@ -245,7 +245,7 @@ def draw_box_lists(tree_plotter, traversal, ibox):
         _draw_box_list(tree_plotter, ibox,
                 traversal.from_sep_smaller_by_level[ilev].starts,
                 traversal.from_sep_smaller_by_level[ilev].lists,
-                key_to_box=traversal.target_boxes,
+                key_to_box=traversal.target_boxes_sep_smaller_by_source_level[ilev],
                 facecolor="orange")
 
     # list 3 close
diff --git a/test/test_traversal.py b/test/test_traversal.py
index 32645a2a708d0f4403a714fdccf69bd654cc7dbe..25ef18f299d4c62f29760dae1fbe04a57709485b 100644
--- a/test/test_traversal.py
+++ b/test/test_traversal.py
@@ -290,9 +290,13 @@ def test_tree_connectivity(ctx_factory, dims, sources_are_targets):
 # }}}
 
 
-# {{{ visualization helper (not a test)
+# {{{ visualization helper
 
-def plot_traversal(ctx_factory, do_plot=False, well_sep_is_n_away=1):
+# Set 'plot' kwarg to True to actually plot. Otherwise, this
+# test simply ensures that interaction list plotting is still
+# working.
+def test_plot_traversal(ctx_factory, well_sep_is_n_away=1, plot=False):
+    pytest.importorskip("matplotlib")
     ctx = ctx_factory()
     queue = cl.CommandQueue(ctx)
 
@@ -337,11 +341,19 @@ def plot_traversal(ctx_factory, do_plot=False, well_sep_is_n_away=1):
         from boxtree.visualization import draw_box_lists
 
         #draw_box_lists(randrange(tree.nboxes))
-        draw_box_lists(plotter, trav, 320)
+
+        if well_sep_is_n_away == 1:
+            draw_box_lists(plotter, trav, 380)
+        elif well_sep_is_n_away == 2:
+            draw_box_lists(plotter, trav, 320)
         #plotter.draw_box_numbers()
 
-        import matplotlib.pyplot as pt
-        pt.show()
+        if plot:
+            import matplotlib.pyplot as pt
+            pt.gca().set_xticks([])
+            pt.gca().set_yticks([])
+
+            pt.show()
 
 # }}}