diff --git a/nn/batch_norm.py b/nn/batch_norm.py
index ba16e8a..621293e 100644
--- a/nn/batch_norm.py
+++ b/nn/batch_norm.py
@@ -229,7 +229,7 @@ def _build_statistics_second_moment(self, input_batch,
         initializer=tf.ones_initializer(),
         trainable=False)
 
-    self._moving_variance = tf.sub(self._moving_second_moment,
+    self._moving_variance = tf.subtract(self._moving_second_moment,
                                    tf.square(self._moving_mean),
                                    name="moving_variance")