--- a/default_plugin/defaultplugin.cpp
+++ b/default_plugin/defaultplugin.cpp
@@ -35,6 +35,7 @@
 #include <iostream>
 #include <sstream>
 #include <stdlib.h>
+#include <unistd.h> /* fork() */
 #include <cstring>
 using namespace std;
 using namespace lineak_core_functions;