diff --git a/selfdrive/controls/lib/longitudinal_mpc_lib/long_mpc.py b/selfdrive/controls/lib/longitudinal_mpc_lib/long_mpc.py
index 7401526364..e0e0208d67 100644
--- a/selfdrive/controls/lib/longitudinal_mpc_lib/long_mpc.py
+++ b/selfdrive/controls/lib/longitudinal_mpc_lib/long_mpc.py
@@ -203,7 +203,7 @@ class LongitudinalMpc():
     self.solver = AcadosOcpSolverFast('long', N, EXPORT_DIR)
     self.v_solution = [0.0 for i in range(N+1)]
     self.a_solution = [0.0 for i in range(N+1)]
-    self.prev_a = self.a_solution
+    self.prev_a = np.array(self.a_solution)
     self.j_solution = [0.0 for i in range(N)]
     self.yref = np.zeros((N+1, COST_DIM))
     for i in range(N):
@@ -371,7 +371,7 @@ class LongitudinalMpc():
     self.a_solution = self.x_sol[:,2]
     self.j_solution = self.u_sol[:,0]
 
-    self.prev_a = interp(T_IDXS + 0.05, T_IDXS, self.a_solution)
+    self.prev_a = np.interp(T_IDXS + 0.05, T_IDXS, self.a_solution)
 
     t = sec_since_boot()
     if self.solution_status != 0: