diff --git a/gio/gportalsupport.h b/gio/gportalsupport.h
index f7bb6ae82..5fe5d8267 100644
--- a/gio/gportalsupport.h
+++ b/gio/gportalsupport.h
@@ -19,6 +19,7 @@
  */
 
 #ifndef __G_PORTAL_SUPPORT_H__
+#define __G_PORTAL_SUPPORT_H__
 
 #include <glib.h>