diff -pur a/src/interface.c b/src/interface.c
--- a/src/interface.c	2012-04-08 11:34:45.000000000 +0200
+++ b/src/interface.c	2021-03-20 12:42:39.420873181 +0100
@@ -12,6 +12,21 @@
 #include "plugin.h"
 #include "interface.h"
 
+/* colour mode frame */
+GtkWidget *lum_toggle;
+
+/* amount/radius frame */
+GtkWidget *amount_label[2], *amount_spin[2];
+GtkWidget *amount_hbox[2], *amount_vbox, *amount_scale[2];
+GtkObject *amount_adj[2];
+
+/* reset buttons */
+GtkWidget *reset_button, *button_hbox;
+
+/* dialog */
+GtkWidget *dialog, *dialog_vbox;
+GtkWidget *preview;
+
 gboolean
 user_interface (GimpDrawable * drawable)
 {
diff -pur a/src/interface.h b/src/interface.h
--- a/src/interface.h	2012-04-08 11:34:45.000000000 +0200
+++ b/src/interface.h	2021-03-20 12:42:49.000843869 +0100
@@ -17,16 +17,16 @@
 /* declare all widgets global to make things a lot easier */
 
 /* colour mode frame */
-GtkWidget *lum_toggle;
+extern GtkWidget *lum_toggle;
 
 /* amount/radius frame */
-GtkWidget *amount_label[2], *amount_spin[2];
-GtkWidget *amount_hbox[2], *amount_vbox, *amount_scale[2];
-GtkObject *amount_adj[2];
+extern GtkWidget *amount_label[2], *amount_spin[2];
+extern GtkWidget *amount_hbox[2], *amount_vbox, *amount_scale[2];
+extern GtkObject *amount_adj[2];
 
 /* reset buttons */
-GtkWidget *reset_button, *button_hbox;
+extern GtkWidget *reset_button, *button_hbox;
 
 /* dialog */
-GtkWidget *dialog, *dialog_vbox;
-GtkWidget *preview;
+extern GtkWidget *dialog, *dialog_vbox;
+extern GtkWidget *preview;
diff -pur a/src/plugin.c b/src/plugin.c
--- a/src/plugin.c	2012-04-08 11:34:45.000000000 +0200
+++ b/src/plugin.c	2021-03-20 12:41:15.047800811 +0100
@@ -11,6 +11,12 @@
 
 #include "plugin.h"
 
+float *fimg[4];
+float *buffer[3];
+gint channels;
+
+GTimer *timer;
+
 GimpPlugInInfo PLUG_IN_INFO = { NULL, NULL, query, run };
 
 MAIN ()
diff -pur a/src/plugin.h b/src/plugin.h
--- a/src/plugin.h	2012-04-08 11:34:45.000000000 +0200
+++ b/src/plugin.h	2021-03-20 12:40:44.667896124 +0100
@@ -67,10 +67,10 @@ typedef struct
 
 extern wavelet_settings settings;
 
-float *fimg[4];
-float *buffer[3];
-gint channels;
+extern float *fimg[4];
+extern float *buffer[3];
+extern gint channels;
 
-GTimer *timer;
+extern GTimer *timer;
 
 #endif /* __PLUGIN_H__ */