diff --git a/learning.py b/learning.py
index 24554ff22..38efcecf2 100644
--- a/learning.py
+++ b/learning.py
@@ -37,7 +37,7 @@ def manhattan_distance(predictions, targets):
 
 
 def mean_boolean_error(predictions, targets):
-    return mean([(p != t) for p, t in zip(predictions, targets)])
+    return mean(int(p != t) for p, t in zip(predictions, targets))
 
 # ______________________________________________________________________________