diff --git a/diffdrr/pose.py b/diffdrr/pose.py
index 92c9dcb2..f3d97e65 100644
--- a/diffdrr/pose.py
+++ b/diffdrr/pose.py
@@ -106,13 +106,13 @@ def get_se3_log(self):
 
 # %% ../notebooks/api/06_pose.ipynb 7
 def make_matrix(R, t):
-    assert (batch_size := len(R)) == len(t)
+    batch_size = len(R)
+    assert batch_size == len(t)
     matrix = torch.zeros(batch_size, 4, 4).to(R)
     matrix[..., :3, :3] = R
     matrix[..., :3, 3] = t
     matrix[..., -1, -1] = 1.0
     return matrix
-
 # %% ../notebooks/api/06_pose.ipynb 8
 from scipy.spatial.transform import Rotation
 
diff --git a/notebooks/api/06_pose.ipynb b/notebooks/api/06_pose.ipynb
index 8555a35e..2aad6d4b 100644
--- a/notebooks/api/06_pose.ipynb
+++ b/notebooks/api/06_pose.ipynb
@@ -198,7 +198,8 @@
    "source": [
     "#| exporti\n",
     "def make_matrix(R, t):\n",
-    "    assert (batch_size := len(R)) == len(t)\n",
+    "    batch_size = len(R)\n",
+    "    assert batch_size == len(t)\n",
     "    matrix = torch.zeros(batch_size, 4, 4).to(R)\n",
     "    matrix[..., :3, :3] = R\n",
     "    matrix[..., :3, 3] = t\n",