diff --git a/lstm.py b/lstm.py
index 05b2fe5..0a76bbf 100644
--- a/lstm.py
+++ b/lstm.py
@@ -251,9 +251,9 @@ def calc_gradient_t(self, t):
         Wfh_grad = np.dot(self.delta_f_list[t], h_prev)
         bf_grad = self.delta_f_list[t]
         Wih_grad = np.dot(self.delta_i_list[t], h_prev)
-        bi_grad = self.delta_f_list[t]
+        bi_grad = self.delta_i_list[t]
         Woh_grad = np.dot(self.delta_o_list[t], h_prev)
-        bo_grad = self.delta_f_list[t]
+        bo_grad = self.delta_o_list[t]
         Wch_grad = np.dot(self.delta_ct_list[t], h_prev)
         bc_grad = self.delta_ct_list[t]
         return Wfh_grad, bf_grad, Wih_grad, bi_grad, \