diff --git a/tensorlayer/layers/activation.py b/tensorlayer/layers/activation.py
index 44fcc47a9..0d50b4a4a 100644
--- a/tensorlayer/layers/activation.py
+++ b/tensorlayer/layers/activation.py
@@ -95,6 +95,7 @@ def build(self, inputs_shape):
     def forward(self, inputs):
 
         pos = tf.nn.relu(inputs)
+        self.alpha_var_constrained = tf.nn.sigmoid(self.alpha_var, name="constraining_alpha_var_in_0_1")
         neg = -self.alpha_var_constrained * tf.nn.relu(-inputs)
 
         return pos + neg