diff --git a/query_strategies/util.py b/query_strategies/util.py
index 819cee4..bc55728 100644
--- a/query_strategies/util.py
+++ b/query_strategies/util.py
@@ -139,10 +139,7 @@ def interleave_offsets(batch, nu):
     groups = [batch // (nu + 1)] * (nu + 1)
     for x in range(batch - sum(groups)):
         groups[-x - 1] += 1
-    offsets = [0]
-    for g in groups:
-        offsets.append(offsets[-1] + g)
-    assert offsets[-1] == batch
+    offsets = [0] + np.cumsum(groups).tolist()
     return offsets
 
 def interleave(xy, batch):