diff --git a/src/4digitdisplay/tm1637.cxx b/src/4digitdisplay/tm1637.cxx
index c7031938..e18068eb 100644
--- a/src/4digitdisplay/tm1637.cxx
+++ b/src/4digitdisplay/tm1637.cxx
@@ -24,6 +24,7 @@
 
 #include <iostream>
 #include <unistd.h>
+#include <stdlib.h>
 
 #include "tm1637.h"
 
diff --git a/src/ledbar/my9221.cxx b/src/ledbar/my9221.cxx
index 054858b0..2bdd17c9 100644
--- a/src/ledbar/my9221.cxx
+++ b/src/ledbar/my9221.cxx
@@ -24,6 +24,7 @@
 
 #include <iostream>
 #include <unistd.h>
+#include <stdlib.h>
 
 #include "my9221.h"
 
diff --git a/src/nrf24l01/nrf24l01.cxx b/src/nrf24l01/nrf24l01.cxx
index 9ad65cbc..fc9c5ab3 100644
--- a/src/nrf24l01/nrf24l01.cxx
+++ b/src/nrf24l01/nrf24l01.cxx
@@ -24,6 +24,7 @@
 
 #include <iostream>
 #include <unistd.h>
+#include <stdlib.h>
 
 #include "nrf24l01.h"