diff --git a/pylipid/func/interactions.py b/pylipid/func/interactions.py
index 5c4237b..e137cfe 100644
--- a/pylipid/func/interactions.py
+++ b/pylipid/func/interactions.py
@@ -100,7 +100,7 @@ def __init__(self, contact_low, contact_high, dt):
         self.contact_low = contact_low
         self.contact_high = contact_high
         self.dt = dt
-        self.pointer = [np.zeros_like(self.contact_high[idx], dtype=np.int)
+        self.pointer = [np.zeros_like(self.contact_high[idx], dtype=np.int64)
                         for idx in range(len(self.contact_high))]
         return
 
diff --git a/requirements.txt b/requirements.txt
index 7dd8414..834d976 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 mdtraj
-numpy
+numpy>=1.2.0
 pandas
 matplotlib>=3.3.3
 networkx