diff --git a/spatialmath/base/transforms3d.py b/spatialmath/base/transforms3d.py
index bc2ceb05..08d3be26 100644
--- a/spatialmath/base/transforms3d.py
+++ b/spatialmath/base/transforms3d.py
@@ -43,7 +43,7 @@
     tr2rt,
     Ab2M,
 )
-from spatialmath.base.quaternions import r2q, q2r, qeye, qslerp
+from spatialmath.base.quaternions import r2q, q2r, qeye, qslerp, qunit
 from spatialmath.base.graphics import plotvol3, axes_logic
 from spatialmath.base.animate import Animate
 import spatialmath.base.symbolic as sym
@@ -1675,7 +1675,7 @@ def trinterp(start, end, s, shortest=True):
             q1 = r2q(end)
             qr = qslerp(q0, q1, s, shortest=shortest)
 
-        return q2r(qr)
+        return q2r(qunit(qr))
 
     elif ismatrix(end, (4, 4)):
         # SE(3) case
@@ -1697,7 +1697,7 @@ def trinterp(start, end, s, shortest=True):
             qr = qslerp(q0, q1, s, shortest=shortest)
             pr = p0 * (1 - s) + s * p1
 
-        return rt2tr(q2r(qr), pr)
+        return rt2tr(q2r(qunit(qr)), pr)
     else:
         return ValueError("Argument must be SO(3) or SE(3)")
 
diff --git a/tests/test_pose3d.py b/tests/test_pose3d.py
index 70b33ce0..fc9daf93 100755
--- a/tests/test_pose3d.py
+++ b/tests/test_pose3d.py
@@ -1389,6 +1389,46 @@ def test_rtvec(self):
         nt.assert_equal(rvec, [0, 1, 0])
         nt.assert_equal(tvec, [2, 3, 4])
 
+    def test_interp(self):
+        # This data is taken from https://github.com/bdaiinstitute/spatialmath-python/issues/165
+        se3_1 = SE3()
+        se3_1.t = np.array(
+            [0.5705748101710814, 0.29623210833184527, 0.10764106509086407]
+        )
+        se3_1.R = np.array(
+            [
+                [0.2852875203191073, 0.9581330588259315, -0.024332536551692617],
+                [0.9582072394229962, -0.28568756930438033, -0.014882844564011068],
+                [-0.021211248608609852, -0.019069722856395098, -0.9995931315303468],
+            ]
+        )
+        assert SE3.isvalid(se3_1.A)
+
+        se3_2 = SE3()
+        se3_2.t = np.array(
+            [0.5150284150005691, 0.25796537207802533, 0.1558725490743694]
+        )
+        se3_2.R = np.array(
+            [
+                [0.42058255728234184, 0.9064420651629983, -0.038380919906699236],
+                [0.9070822373513454, -0.4209501599465646, -0.0016665901233428627],
+                [-0.01766712176680449, -0.0341137119645545, -0.9992617912561634],
+            ]
+        )
+        assert SE3.isvalid(se3_2.A)
+
+        path_se3 = se3_1.interp(end=se3_2, s=15, shortest=False)
+
+        angle = None
+        for i in range(len(path_se3) - 1):
+            assert SE3.isvalid(path_se3[i].A)
+
+            if angle is None:
+                angle = path_se3[i].angdist(path_se3[i + 1])
+            else:
+                test_angle = path_se3[i].angdist(path_se3[i + 1])
+                assert abs(test_angle - angle) < 1e-6
+
 
 # ---------------------------------------------------------------------------------------#
 if __name__ == "__main__":