diff --git a/openselfsup/third_party/clustering.py b/openselfsup/third_party/clustering.py
index d84459b0..e1a1ff63 100644
--- a/openselfsup/third_party/clustering.py
+++ b/openselfsup/third_party/clustering.py
@@ -5,6 +5,7 @@ import time
 import numpy as np
 import faiss
 import torch
+from scipy.sparse import csr_matrix
 
 __all__ = ['Kmeans', 'PIC']