diff --git a/src/caffe/layers/sigmoid_layer.cpp b/src/caffe/layers/sigmoid_layer.cpp
index 85fd9676812..f8aa769a174 100644
--- a/src/caffe/layers/sigmoid_layer.cpp
+++ b/src/caffe/layers/sigmoid_layer.cpp
@@ -7,7 +7,7 @@ namespace caffe {
 
 template <typename Dtype>
 inline Dtype sigmoid(Dtype x) {
-  return 1. / (1. + exp(-x));
+  return 0.5 * tanh(0.5 * x) + 0.5;
 }
 
 template <typename Dtype>