diff --git a/src/jsrm/systems/planar_pcs.py b/src/jsrm/systems/planar_pcs.py
index 5dbeab9..0c45c81 100644
--- a/src/jsrm/systems/planar_pcs.py
+++ b/src/jsrm/systems/planar_pcs.py
@@ -409,7 +409,7 @@ def energy_fn(params: Dict[str, Array], q: Array, q_d: Array) -> Array:
         Returns:
             E: total energy of shape ()
         """
-        T = kinetic_energy_fn(params, q_d)
+        T = kinetic_energy_fn(params, q, q_d)
         U = potential_energy_fn(params, q)
         E = T + U