diff --git a/src/udp_engine.cpp b/src/udp_engine.cpp
index 9d1210ac..3104cdad 100644
--- a/src/udp_engine.cpp
+++ b/src/udp_engine.cpp
@@ -4,6 +4,7 @@
 #include "windows.hpp"
 #else
 #include <sys/types.h>
+#include <unistd.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>