diff --git a/qiskit_dynamics/arraylias/register_functions/multiply.py b/qiskit_dynamics/arraylias/register_functions/multiply.py
index c1b8002c9..77977c6f0 100644
--- a/qiskit_dynamics/arraylias/register_functions/multiply.py
+++ b/qiskit_dynamics/arraylias/register_functions/multiply.py
@@ -18,7 +18,7 @@
 
 
 def register_multiply(alias):
-    """register multiply functions to each array libraries"""
+    """Register multiply functions to each array library."""
 
     @alias.register_function(lib="scipy_sparse", path="multiply")
     def _(x, y):