diff --git a/src/qibo/quantum_info/entropies.py b/src/qibo/quantum_info/entropies.py
index 3d4e7ac027..842fa82e47 100644
--- a/src/qibo/quantum_info/entropies.py
+++ b/src/qibo/quantum_info/entropies.py
@@ -1,4 +1,4 @@
-"""Submodule with entropy measures."""
+""Submodule with entropy measures."""
 
 from typing import Union
 
@@ -461,7 +461,7 @@ def von_neumann_entropy(
 
     if purity(state) == 1.0:
         if return_spectrum:
-            return 0.0, backend.cast([1.0], dtype=float)
+            return 0.0, backend.cast([0.0], dtype=float)
 
         return 0.0