diff --git a/find_dupes.py b/find_dupes.py
index d2b9ba2..097598f 100644
--- a/find_dupes.py
+++ b/find_dupes.py
@@ -134,8 +134,8 @@ def main():
     # 'same show, different shot'.
     close = ham <= args.max_dist
 
-    amat = np.array([data[f][1] for f in names], dtype=np.int64)
-    xa = (amat[:, None] ^ amat[None, :])
+    amat = np.array([data[f][1] for f in names], dtype=np.uint64)
+    xa = (amat[:, None] ^ amat[None, :]).astype(np.int64)
     aham = np.zeros(xa.shape, dtype=np.int16)
     for b in range(64):
         aham += ((xa >> b) & 1).astype(np.int16)