diff --git a/ooni/inputunit.py b/ooni/inputunit.py
index 2e80940ff..fb85d9eaa 100644
--- a/ooni/inputunit.py
+++ b/ooni/inputunit.py
@@ -38,7 +38,7 @@ def __len__(self):
         Returns the number of input units in the input unit factory.
         """
         if not self.length:
-            self.length = ceil(sum(1 for _ in self._inputs)/self.inputUnitSize)
+            self.length = ceil(float(sum(1 for _ in self._inputs))/self.inputUnitSize)
         return self.length
 
     def next(self):