diff --git a/jaxopt/_src/osqp.py b/jaxopt/_src/osqp.py
index 7eae7f86..6d47e6bb 100644
--- a/jaxopt/_src/osqp.py
+++ b/jaxopt/_src/osqp.py
@@ -31,7 +31,7 @@
 from jaxopt._src import base
 from jaxopt._src import implicit_diff as idf
 from jaxopt._src.cond import cond
-from jaxopt.tree_util import tree_add, tree_sub, tree_mul
+from jaxopt.tree_util import tree_add, tree_sub, tree_mul, tree_sum
 from jaxopt.tree_util import tree_scalar_mul, tree_add_scalar_mul
 from jaxopt.tree_util import tree_map, tree_vdot
 from jaxopt.tree_util import tree_ones_like, tree_zeros_like, tree_where
@@ -792,7 +792,7 @@ def matvec_Q(params_obj, x):
         # nabla_x f(x) = Q x + c
         # Qx = nabla_x f(x) - c
         def fun_minus_cx(xx):
-          return self.fun(xx, params_Q) - jnp.sum(c*xx)
+          return self.fun(xx, params_Q) - tree_sum(tree_mul(c, xx))
         Qx = jax.grad(fun_minus_cx)(x)
         return Qx
       self.matvec_Q = matvec_Q