diff --git a/modules/util/util.py b/modules/util/util.py
index dd715f5207a4653da4616637d78a874e8850d001..5c90a935afda3f7b5e6719f7ce09b4ebabceb277 100644
--- a/modules/util/util.py
+++ b/modules/util/util.py
@@ -202,7 +202,7 @@ def find_bin_index(nda, value_s):
         iL = idxs[above].max()
         iL_s[k] = iL
 
-    return iL_s
+    return iL_s.astype(np.int32)
 
 
 # array solzen must be degrees, missing values must NaN. For small roughly 50x50km regions only