From 6dec9abffea7a3d5b6ca137bee2f55d21b7c9261 Mon Sep 17 00:00:00 2001
From: Davis King <davis@dlib.net>
Date: Fri, 5 Jul 2019 11:46:32 -0400
Subject: [PATCH] Added missing include

---
 dlib/optimization/isotonic_regression.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/dlib/optimization/isotonic_regression.h b/dlib/optimization/isotonic_regression.h
index 4f14299c9..3717f8bd5 100644
--- a/dlib/optimization/isotonic_regression.h
+++ b/dlib/optimization/isotonic_regression.h
@@ -6,6 +6,7 @@
 #include "isotonic_regression_abstract.h"
 #include <vector>
 #include <utility>
+#include <cstddef>
 
 namespace dlib
 {