diff --git a/mlp/errors.py b/mlp/errors.py
index a61b757..0b0d603 100644
--- a/mlp/errors.py
+++ b/mlp/errors.py
@@ -154,9 +154,9 @@ class CrossEntropySoftmaxError(object):
         Returns:
             Scalar error function value.
         """
-        probs = np.exp(outputs - outputs.max(-1)[:, None])
-        probs /= probs.sum(-1)[:, None]
-        return -np.mean(np.sum(targets * np.log(probs), axis=1))
+        normOutputs = outputs - outputs.max(-1)[:, None]
+        logProb = normOutputs - np.log(np.sum(np.exp(normOutputs))(-1)[:, None])
+        return -np.mean(np.sum(targets * logProb, axis=1))
 
     def grad(self, outputs, targets):
         """Calculates gradient of error function with respect to outputs.