diff --git a/service/models/operations/optimize.py b/service/models/operations/optimize.py
index 3acdfce..3ca21c0 100644
--- a/service/models/operations/optimize.py
+++ b/service/models/operations/optimize.py
@@ -61,7 +61,7 @@ def gen_risk_bound(self):
 
 def objfun(x, initial_guess, objective_function_option, relative_importance):
     total_sum = 0
-    sum_of_all_weights = sum(relative_importance)
+    sum_of_all_weights = np.sum(relative_importance)
 
     for i in range(len(x)):
         weight = relative_importance[i] / sum_of_all_weights