diff --git a/Python/ml_metrics/average_precision.py b/Python/ml_metrics/average_precision.py
index e18297d..4e4f90a 100644
--- a/Python/ml_metrics/average_precision.py
+++ b/Python/ml_metrics/average_precision.py
@@ -33,7 +33,7 @@ def apk(actual, predicted, k=10):
             num_hits += 1.0
             score += num_hits / (i+1.0)
 
-    if not actual:
+    if len(actual) == 0:
         return 0.0
 
     return score / min(len(actual), k)