diff --git a/gtk/gtkmain.c b/gtk/gtkmain.c
index 35a1dc5921..d0122f3bcb 100644
--- a/gtk/gtkmain.c
+++ b/gtk/gtkmain.c
@@ -36,6 +36,9 @@
 #include <stdlib.h>
 #include <string.h>
 #include <gmodule.h>
+#ifdef G_OS_UNIX
+#include <unistd.h>
+#endif
 #include "gtkdnd.h"
 #include "gtkcompat.h"
 #include "gtkmain.h"