diff --git a/tensorpack/coupled.py b/tensorpack/coupled.py
index fab8342..52648c4 100644
--- a/tensorpack/coupled.py
+++ b/tensorpack/coupled.py
@@ -253,7 +253,7 @@ def normalize_factors(self, method="max"):
         for mmode in self.modes:
             sol = self.x["_" + mmode]
             if method == "max":     # the one with maximum absolute value
-                norm_vec = np.array([max(sol[:, ii].min(), sol[:, ii].max(), key=abs) for ii in range(sol.shape[1])])
+                norm_vec = abs(sol).max(axis=0).to_numpy()
             elif method == "norm":
                 norm_vec = norm(sol, axis=0)
             else: