diff --git a/lib/roi_pooling_layer/roi_pooling_op_grad.py b/lib/roi_pooling_layer/roi_pooling_op_grad.py
index 8f03f7e..262efcf 100644
--- a/lib/roi_pooling_layer/roi_pooling_op_grad.py
+++ b/lib/roi_pooling_layer/roi_pooling_op_grad.py
@@ -1,5 +1,6 @@
 import tensorflow as tf
 from tensorflow.python.framework import ops
+import roi_pooling_op
 
 @ops.RegisterGradient("RoiPool")
 def _roi_pool_grad(op, grad, _):