diff --git a/social_mpc/mpc.py b/social_mpc/mpc.py
index 09af48737b9e1d202db8c083c5a8af81a59ec6d5..89314ef5656c3e65dadea64c146c91d57b643033 100644
--- a/social_mpc/mpc.py
+++ b/social_mpc/mpc.py
@@ -149,7 +149,7 @@ class MPC:
         if cost_map is not None:
             assert(cost_map.shape == self.cost_map_dim)
         if reg_parameter is not None:
-            assert(len(reg_parameter) == self.action_dim or np.isscalar(isscalar))
+            assert(len(reg_parameter) == self.action_dim or np.isscalar(reg_parameter))
         if goto_goal is not None:
             assert(len(goto_goal) == self.goto_target_dim)
         if pan_goal is not None: