diff --git a/src/LocalMapping.cc b/src/LocalMapping.cc
index 6c87a6e55a..64038fd541 100644
--- a/src/LocalMapping.cc
+++ b/src/LocalMapping.cc
@@ -22,7 +22,7 @@
 #include "LoopClosing.h"
 #include "ORBmatcher.h"
 #include "Optimizer.h"
-
+#include <unistd.h>
 #include<mutex>
 
 namespace ORB_SLAM2
diff --git a/src/LoopClosing.cc b/src/LoopClosing.cc
index 5e317dd420..0c6beb0997 100644
--- a/src/LoopClosing.cc
+++ b/src/LoopClosing.cc
@@ -27,7 +27,7 @@
 #include "Optimizer.h"
 
 #include "ORBmatcher.h"
-
+#include <unistd.h>
 #include<mutex>
 #include<thread>
 
diff --git a/src/System.cc b/src/System.cc
index 8df4157095..0d7a2a5c7a 100644
--- a/src/System.cc
+++ b/src/System.cc
@@ -22,6 +22,7 @@
 
 #include "System.h"
 #include "Converter.h"
+#include <unistd.h>
 #include <thread>
 #include <pangolin/pangolin.h>
 #include <iomanip>
diff --git a/src/Tracking.cc b/src/Tracking.cc
index 2273b2ce48..57a45f9ae8 100644
--- a/src/Tracking.cc
+++ b/src/Tracking.cc
@@ -32,7 +32,7 @@
 
 #include"Optimizer.h"
 #include"PnPsolver.h"
-
+#include <unistd.h>
 #include<iostream>
 
 #include<mutex>
diff --git a/src/Viewer.cc b/src/Viewer.cc
index dec3204f53..967c627df6 100644
--- a/src/Viewer.cc
+++ b/src/Viewer.cc
@@ -20,7 +20,7 @@
 
 #include "Viewer.h"
 #include <pangolin/pangolin.h>
-
+#include <unistd.h>
 #include <mutex>
 
 namespace ORB_SLAM2