diff --git a/qiskit/algorithms/gradients/lin_comb_sampler_gradient.py b/qiskit/algorithms/gradients/lin_comb_sampler_gradient.py
index 0f4cf0631e97..2a2af2dd8df6 100644
--- a/qiskit/algorithms/gradients/lin_comb_sampler_gradient.py
+++ b/qiskit/algorithms/gradients/lin_comb_sampler_gradient.py
@@ -114,8 +114,10 @@ def _run(
             n = 2 ** circuits[i].num_qubits
             grad_dists = np.zeros((len(metadata_[i]["parameters"]), n))
             for idx, coeff, dist in zip(result_indices_all[i], coeffs_all[i], result.quasi_dists):
-                grad_dists[idx][list(dist.keys())[:n]] += np.array(list(dist.values())[:n]) * coeff
-                grad_dists[idx][list(dist.keys())[:n]] -= np.array(list(dist.values())[n:]) * coeff
+                plus = {key: val for key, val in dist.items() if key < n}
+                minus = {key - n: val for key, val in dist.items() if key >= n}
+                grad_dists[idx][list(plus.keys())] += np.fromiter(plus.values(), dtype=float) * coeff
+                grad_dists[idx][list(minus.keys())] -= np.fromiter(minus.values(), dtype=float) * coeff
 
             gradient_ = []
             for grad_dist in grad_dists: