diff --git a/DMRNetwork.cpp b/DMRNetwork.cpp
index 15bf3bc..ede4a5a 100644
--- a/DMRNetwork.cpp
+++ b/DMRNetwork.cpp
@@ -26,6 +26,7 @@
 #include <cstdio>
 #include <cassert>
 #include <cstring>
+#include <stdlib.h>
 
 const unsigned int BUFFER_LENGTH = 500U;
 
diff --git a/DStarNetwork.cpp b/DStarNetwork.cpp
index 443fcac..8da0740 100644
--- a/DStarNetwork.cpp
+++ b/DStarNetwork.cpp
@@ -26,6 +26,7 @@
 #include <cstdio>
 #include <cassert>
 #include <cstring>
+#include <stdlib.h>
 
 const unsigned int BUFFER_LENGTH = 100U;
 
diff --git a/MMDVMHost.cpp b/MMDVMHost.cpp
index 3eef883..8f3594f 100644
--- a/MMDVMHost.cpp
+++ b/MMDVMHost.cpp
@@ -46,6 +46,7 @@
 
 #include <cstdio>
 #include <vector>
+#include <stdlib.h>
 
 #if !defined(_WIN32) && !defined(_WIN64)
 #include <sys/types.h>