diff --git a/diffdrr/pose.py b/diffdrr/pose.py
index ae4903c7c..1cbdadd59 100644
--- a/diffdrr/pose.py
+++ b/diffdrr/pose.py
@@ -19,7 +19,7 @@ class RigidTransform(torch.nn.Module):
 
     def __init__(self, matrix):
         super().__init__()
-        if specimen.extrinsic.matrix.dim() == 2:
+        if matrix.dim() == 2:
             matrix = matrix.unsqueeze(0)
         self.register_buffer("matrix", matrix)
 
@@ -39,7 +39,7 @@ def inverse(self):
         t = self.matrix[..., :3, 3]
         Rinv = R.mT
         tinv = -torch.einsum("bij, bj -> bi", Rinv, t)
-        make_matrix(Rinv, tinv)
+        matrix = make_matrix(Rinv, tinv)
         return RigidTransform(matrix)
 
     def compose(self, T):
diff --git a/notebooks/api/06_pose.ipynb b/notebooks/api/06_pose.ipynb
index 0ae9716c1..6f85a1dfa 100644
--- a/notebooks/api/06_pose.ipynb
+++ b/notebooks/api/06_pose.ipynb
@@ -95,7 +95,7 @@
     "\n",
     "    def __init__(self, matrix):\n",
     "        super().__init__()\n",
-    "        if specimen.extrinsic.matrix.dim() == 2:\n",
+    "        if matrix.dim() == 2:\n",
     "            matrix = matrix.unsqueeze(0)\n",
     "        self.register_buffer(\"matrix\", matrix)\n",
     "\n",
@@ -115,7 +115,7 @@
     "        t = self.matrix[..., :3, 3]\n",
     "        Rinv = R.mT\n",
     "        tinv = -torch.einsum(\"bij, bj -> bi\", Rinv, t)\n",
-    "        make_matrix(Rinv, tinv)\n",
+    "        matrix = make_matrix(Rinv, tinv)\n",
     "        return RigidTransform(matrix)\n",
     "\n",
     "    def compose(self, T):\n",