https://gitlab.gnome.org/GNOME/vinagre/-/commit/2fab741dd1b9443f453aba880e55beffa364f453?merge_request_iid=8

diff --git a/plugins/vnc/vinagre-vnc-connection.c b/plugins/vnc/vinagre-vnc-connection.c
index ac8bbb33ff1440c0499c0bee6b8d54e76b20a6f7..0a3334ea772342934f8bd17b4d125786e534707b 100644
--- a/plugins/vnc/vinagre-vnc-connection.c
+++ b/plugins/vnc/vinagre-vnc-connection.c
@@ -27,6 +27,8 @@
 #include "vinagre-vnc-connection.h"
 #include "vinagre-vala.h"
 
+gboolean scaling_command_line;
+
 struct _VinagreVncConnectionPrivate
 {
   gchar    *desktop_name;
diff --git a/plugins/vnc/vinagre-vnc-connection.h b/plugins/vnc/vinagre-vnc-connection.h
index 4788ae20f47365a13b6bfc3383d6492b75d90025..f37642cb4807efa31c4d4d533d04bd15342e9240 100644
--- a/plugins/vnc/vinagre-vnc-connection.h
+++ b/plugins/vnc/vinagre-vnc-connection.h
@@ -26,7 +26,7 @@
 
 G_BEGIN_DECLS
 
-gboolean scaling_command_line;
+extern gboolean scaling_command_line;
 
 #define VINAGRE_TYPE_VNC_CONNECTION             (vinagre_vnc_connection_get_type ())
 #define VINAGRE_VNC_CONNECTION(obj)             (G_TYPE_CHECK_INSTANCE_CAST ((obj), VINAGRE_TYPE_VNC_CONNECTION, VinagreVncConnection))