diff --git a/spatialmath/quaternion.py b/spatialmath/quaternion.py
index be0ea2f0..26d8093a 100644
--- a/spatialmath/quaternion.py
+++ b/spatialmath/quaternion.py
@@ -77,6 +77,9 @@ def __init__(self, s: Any = None, v=None, check: Optional[bool] = True):
         """
         super().__init__()
 
+        if s is None and smb.isvector(v, 4):
+            v,s = (s,v)
+
         if v is None:
             # single argument
             if super().arghandler(s, check=False):
@@ -979,6 +982,11 @@ def __init__(
         """
         super().__init__()
 
+        # handle: UnitQuaternion(v)`` constructs a unit quaternion with specified elements 
+        # from ``v`` which is a 4-vector given as a list, tuple, or ndarray(4)
+        if s is None and smb.isvector(v, 4):
+            v,s = (s,v)
+
         if v is None:
             # single argument
             if super().arghandler(s, check=check):
diff --git a/tests/test_quaternion.py b/tests/test_quaternion.py
index 0f2ac871..791e27bf 100644
--- a/tests/test_quaternion.py
+++ b/tests/test_quaternion.py
@@ -70,6 +70,9 @@ def test_constructor(self):
         qcompare(UnitQuaternion(2, [0, 0, 0]), np.r_[1, 0, 0, 0])
         qcompare(UnitQuaternion(-2, [0, 0, 0]), np.r_[1, 0, 0, 0])
 
+        qcompare(UnitQuaternion([1, 2, 3, 4]), UnitQuaternion(v = [1, 2, 3, 4]))
+        qcompare(UnitQuaternion(s = 1, v = [2, 3, 4]), UnitQuaternion(v = [1, 2, 3, 4]))
+
         # from R
 
         qcompare(UnitQuaternion(np.eye(3)), [1, 0, 0, 0])
@@ -753,6 +756,9 @@ def test_constructor(self):
         nt.assert_array_almost_equal(Quaternion(2, [0, 0, 0]).vec, [2, 0, 0, 0])
         nt.assert_array_almost_equal(Quaternion(-2, [0, 0, 0]).vec, [-2, 0, 0, 0])
 
+        qcompare(Quaternion([1, 2, 3, 4]), Quaternion(v = [1, 2, 3, 4]))
+        qcompare(Quaternion(s = 1, v = [2, 3, 4]), Quaternion(v = [1, 2, 3, 4]))
+
         # pure
         v = [5, 6, 7]
         nt.assert_array_almost_equal(