diff --git a/source/net_udp.c b/source/net_udp.c
index aa90d8a..86b04ee 100644
--- a/source/net_udp.c
+++ b/source/net_udp.c
@@ -41,6 +41,10 @@
 #include <string.h>
 #include <stdlib.h>
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #ifdef __sun__
 #include <sys/filio.h>
 #endif