diff --git a/vmodel/geometry.py b/vmodel/geometry.py
index e066aa4..a16a734 100644
--- a/vmodel/geometry.py
+++ b/vmodel/geometry.py
@@ -33,7 +33,7 @@ def voronoi_neighbors(positions: np.ndarray) -> list:
     """
     tri = Delaunay(positions)
     neighbors = defaultdict(set)
-    for p in tri.vertices:
+    for p in tri.simplices:
         for i, j in combinations(p, 2):
             neighbors[i].add(j)
             neighbors[j].add(i)
diff --git a/vmodel/plot.py b/vmodel/plot.py
index f120722..c8eabbb 100644
--- a/vmodel/plot.py
+++ b/vmodel/plot.py
@@ -390,7 +390,7 @@ def voronoi_plot_2d(vor, ax=None, **kw):
     line_style = kw.get('line_style', 'solid')
 
     center = vor.points.mean(axis=0)
-    ptp_bound = vor.points.ptp(axis=0)
+    ptp_bound = np.ptp(vor.points, axis=0))
 
     finite_segments = []
     infinite_segments = []