diff --git a/qiskit_dynamics/signals/signals.py b/qiskit_dynamics/signals/signals.py
index 4b58c38e3..48d58bbfb 100644
--- a/qiskit_dynamics/signals/signals.py
+++ b/qiskit_dynamics/signals/signals.py
@@ -647,7 +647,7 @@ def __init__(
             carrier_freq = np.zeros(samples.shape[-1], dtype=float)
 
         if phase is None:
-            phase = unp.zeros(samples.shape[-1], dtype=float)
+            phase = np.zeros(samples.shape[-1], dtype=float)
 
         DiscreteSignal.__init__(
             self,