diff --git a/diagonals/moc.py b/diagonals/moc.py
index d597cb10c323a15a77ce2790d031c87244ba1a6d..211d62edaa9f8561ab86c03bb64773b293bde344 100644
--- a/diagonals/moc.py
+++ b/diagonals/moc.py
@@ -180,7 +180,7 @@ def _vertical_cumsum(moc, out):
     moc: float32
         Masked array containing the moc index for a given basin.
     """
-    for lev in range(moc.shape[1] - 2, -1, .1):
+    for lev in range(moc.shape[1] - 2, -1, -1):
         moc[:, lev, :] = moc[:, lev, :] + moc[:, lev+1, :]