diff --git a/uproot/write/objects/TH.py b/uproot/write/objects/TH.py
index 298b3c90..c86fa62f 100644
--- a/uproot/write/objects/TH.py
+++ b/uproot/write/objects/TH.py
@@ -74,7 +74,7 @@ def __init__(self, histogram):
         else:
             raise ValueError("unrecognized histogram class name {0}".format(self.fClassName))
 
-        self.fields["_fNcells"] = len(self.valuesarray)
+        self.fields["_fNcells"] = self.valuesarray.size
         self.fields["_fContour"] = numpy.array(self.fields["_fContour"], dtype=">f8", copy=False)
         self.fields["_fSumw2"] = numpy.array(self.fields["_fSumw2"], dtype=">f8", copy=False)