diff --git a/src/qibo/backends/abstract.py b/src/qibo/backends/abstract.py
index 14d1dc752c..4d06d6ef9a 100644
--- a/src/qibo/backends/abstract.py
+++ b/src/qibo/backends/abstract.py
@@ -326,13 +326,21 @@ def entanglement_entropy(self, rho):  # pragma: no cover
         raise_error(NotImplementedError)
 
     @abc.abstractmethod
-    def calculate_norm(self, state):  # pragma: no cover
-        """Calculate norm of a state vector."""
+    def calculate_norm(self, state, ord=None):  # pragma: no cover
+        """Calculate norm of a state vector.
+
+        For specifications on possible values of the parameter `ord`, please refer to
+        `numpy.linalg.norm <https://numpy.org/doc/stable/reference/generated/numpy.linalg.norm.html>`_.
+        """
         raise_error(NotImplementedError)
 
     @abc.abstractmethod
-    def calculate_norm_density_matrix(self, state):  # pragma: no cover
-        """Calculate norm (trace) of a density matrix."""
+    def calculate_norm_density_matrix(self, state, ord="nuc"):  # pragma: no cover
+        """Calculate norm (trace) of a density matrix.
+
+        For specifications on possible values of the parameter `ord`, please refer to
+        `numpy.linalg.norm <https://numpy.org/doc/stable/reference/generated/numpy.linalg.norm.html>`_.
+        """
         raise_error(NotImplementedError)
 
     @abc.abstractmethod