diff --git a/scispacy/candidate_generation.py b/scispacy/candidate_generation.py
index 7bcf934..00324ac 100644
--- a/scispacy/candidate_generation.py
+++ b/scispacy/candidate_generation.py
@@ -281,8 +281,8 @@ def nmslib_knn_with_zero_vectors(
         neighbors.append([])
         distances.append([])
         # interleave `neighbors` and Nones in `extended_neighbors`
-        extended_neighbors[empty_vectors_boolean_flags] = numpy.array(neighbors)[:-1]
-        extended_distances[empty_vectors_boolean_flags] = numpy.array(distances)[:-1]
+        extended_neighbors[empty_vectors_boolean_flags] = numpy.array(neighbors, dtype='object')[:-1]
+        extended_distances[empty_vectors_boolean_flags] = numpy.array(distances, dtype='object')[:-1]
 
         return extended_neighbors, extended_distances