diff --git a/src/unix/gsocket.c b/src/unix/gsocket.c
index ef6f652c77..4157d89baa 100644
--- a/src/unix/gsocket.c
+++ b/src/unix/gsocket.c
@@ -28,6 +28,7 @@
 #include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stddef.h>
 #include <ctype.h>
 
 #ifdef sun