diff --git a/paddle/operators/prior_box_op.h b/paddle/operators/prior_box_op.h
index 5483dd7bbe9a4aad91aca86442eab4e35a28b0d5..1869807dc89ab100607d0a7732e828ced84e7c0f 100644
--- a/paddle/operators/prior_box_op.h
+++ b/paddle/operators/prior_box_op.h
@@ -165,7 +165,7 @@ class PriorBoxOpKernel : public framework::OpKernel<T> {
     }
 
     Eigen::Tensor<T, 2, Eigen::RowMajor> var_et(1, variances.size());
-    for (int i = 0; i < variances.size(); ++i) {
+    for (size_t i = 0; i < variances.size(); ++i) {
       var_et(0, i) = variances[i];
     }