diff --git a/tn.py b/tn.py
index 9464fe7..03283f5 100644
--- a/tn.py
+++ b/tn.py
@@ -110,7 +110,7 @@ def tn(sims: np.ndarray,
 
             # Constraints C3
             if len(intermediate_rs) == 0:
-                C3 = np.ones(C2.shape, dtype=np.bool)
+                C3 = np.ones(C2.shape, dtype=bool)
             else:
                 # "the equal sign" in C3 in paper is wrong because it's contradictory to C2
                 cond1 = intermediate_rs[None, :] > r_i[:, None]