diff --git a/mjx/mujoco/mjx/_src/types.py b/mjx/mujoco/mjx/_src/types.py
index faf47012..e29d4aca 100644
--- a/mjx/mujoco/mjx/_src/types.py
+++ b/mjx/mujoco/mjx/_src/types.py
@@ -775,6 +775,7 @@ class Model(PyTreeNode):
   mesh_texcoord: np.ndarray
   flex_vertadr: np.ndarray
   flex_vertnum: np.ndarray
+  flex_interp: np.ndarray
   flex_vert0: np.ndarray
   flex_nodeadr: np.ndarray
   flex_nodenum: np.ndarray