diff --git a/include/surface_normal.h b/include/surface_normal.h
index 0a39ab7..f2e97bc 100644
--- a/include/surface_normal.h
+++ b/include/surface_normal.h
@@ -1,7 +1,5 @@
 #pragma once
 
-#include <vector>
-
 #include <opencv2/core.hpp>
 
 using Plane = cv::Vec4f;
@@ -18,6 +16,6 @@ cv::Mat3f normals_from_depth(const cv::Mat1f &depth, CameraIntrinsics intrinsics
 cv::Mat3b normals_to_rgb(const cv::Mat3f &normals);
 
 cv::Mat1f get_surrounding_points(const cv::Mat1f &depth, int i, int j, CameraIntrinsics intrinsics,
-                                 size_t window_size, float max_rel_depth_diff);
+                                 int window_size, float max_rel_depth_diff);
 
 cv::Vec3f fit_plane(const cv::Mat &points);
diff --git a/src/surface_normal.cpp b/src/surface_normal.cpp
index 938ea72..8b2f2d0 100644
--- a/src/surface_normal.cpp
+++ b/src/surface_normal.cpp
@@ -1,14 +1,15 @@
-#include <vector>
+#include <cmath>
 
 #include <opencv2/core.hpp>
 
 #include "surface_normal.h"
 
 using namespace cv;
+using std::abs;
 
 // Returns a Nx3 matrix of 3D points surrounding the i,j pixel within the window_size window.
 Mat1f get_surrounding_points(const Mat1f &depth, int i, int j, CameraIntrinsics intrinsics,
-                             size_t window_size, float max_rel_depth_diff) {
+                             int window_size, float max_rel_depth_diff) {
   float f_inv        = 1.f / intrinsics.f;
   float cx           = intrinsics.cx;
   float cy           = intrinsics.cy;