diff --git a/modopt/opt/algorithms/admm.py b/modopt/opt/algorithms/admm.py
index b881b770..23d382b4 100644
--- a/modopt/opt/algorithms/admm.py
+++ b/modopt/opt/algorithms/admm.py
@@ -38,7 +38,10 @@ def __init__(self, cost_funcs, A, B, b, tau, **kwargs):
         self.B = B
         self.b = b
         self.tau = tau
-
+        if self.A is self.B:
+            self.AuplusBv = lambda u, v: self.A.op(u + v)
+        else:
+            self.AuplusBv = lambda u, v: self.A.op(u) + self.B.op(v)
     def _calc_cost(self, u, v, **kwargs):
         """Calculate the cost.
 
@@ -60,7 +63,7 @@ def _calc_cost(self, u, v, **kwargs):
         xp = get_array_module(u)
         cost = self.cost_funcs[0](u)
         cost += self.cost_funcs[1](v)
-        cost += self.tau * xp.linalg.norm(self.A.op(u) + self.B.op(v) - self.b)
+        cost += self.tau * xp.linalg.norm(self.AuplusBv(u,v) - self.b)
         return cost
 
 
diff --git a/modopt/opt/algorithms/forward_backward.py b/modopt/opt/algorithms/forward_backward.py
index 702799c6..d81bcde8 100644
--- a/modopt/opt/algorithms/forward_backward.py
+++ b/modopt/opt/algorithms/forward_backward.py
@@ -955,7 +955,11 @@ def _update(self):
         t_shifted_ratio = (self._t_old - 1) / self._t_new
         sigma_t_ratio = self._sigma * self._t_old / self._t_new
         beta_xi_t_shifted_ratio = t_shifted_ratio * self._beta / self._xi
-        self._z = - beta_xi_t_shifted_ratio * (self._x_old - self._z)
+
+        #self._z = - beta_xi_t_shifted_ratio * (self._x_old - self._z)
+        self._z -= self._x_old
+        self._z *= beta_xi_t_shifted_ratio
+
         self._z += self._u_new
         self._z += t_shifted_ratio * (self._u_new - self._u_old)
         self._z += sigma_t_ratio * (self._u_new - self._x_old)