diff --git a/evoc/cluster_trees.py b/evoc/cluster_trees.py
index 8350d90..f7b5ab0 100644
--- a/evoc/cluster_trees.py
+++ b/evoc/cluster_trees.py
@@ -150,7 +150,7 @@ def condense_tree(hierarchy, min_cluster_size=10):
     lambdas = np.empty(root, dtype=np.float32)
     sizes = np.ones(root, dtype=np.int64)
 
-    ignore = np.zeros(root + 1, dtype=np.bool)
+    ignore = np.zeros(root + 1, dtype=np.bool_)
 
     idx = 0