diff -up bogl-0.1.18/bogl.c.orig bogl-0.1.18/bogl.c
--- bogl-0.1.18/bogl.c.orig	2020-02-17 13:01:42.862405559 +0100
+++ bogl-0.1.18/bogl.c	2020-02-17 13:04:37.126782135 +0100
@@ -107,6 +107,24 @@ static void kbd_done (void);
 static void vt_switch (int);
 
 static struct fb_fix_screeninfo fb_fix;
+
+/* Device-specific routines. */
+
+void (*bogl_pixel) (int x, int y, int c);
+void (*bogl_hline) (int x1, int x2, int y, int c);
+void (*bogl_vline) (int x, int y1, int y2, int c);
+void (*bogl_text) (int x, int y, const char *s, int n, int fg, int bg, int ul,
+                   const struct bogl_font *font);
+void (*bogl_clear) (int x1, int y1, int x2, int y2, int c);
+void (*bogl_move) (int sx, int sy, int dx, int dy, int w, int h);
+void (*bogl_put) (int x, int y, const struct bogl_pixmap *pixmap,
+                  const int color_map[16]);
+void (*bogl_pointer) (int visible, int x, int y,
+                      const struct bogl_pointer *,
+                      int colors[2]);
+void (*bogl_set_palette) (int c, int nc, const unsigned char palette[][3]);
+void (*bogl_reinit) (void);
+
 /* Initialize BOGL. */
 int
 bogl_init (void)
diff -up bogl-0.1.18/bogl.h.orig bogl-0.1.18/bogl.h
--- bogl-0.1.18/bogl.h.orig	2004-05-06 04:57:06.000000000 +0200
+++ bogl-0.1.18/bogl.h	2020-02-17 13:01:42.867405570 +0100
@@ -86,19 +86,19 @@ int bogl_font_glyph (const struct bogl_f
 int bogl_in_font (const struct bogl_font *font, wchar_t wc);
 
 /* Device-specific routines. */
-void (*bogl_pixel) (int x, int y, int c);
-void (*bogl_hline) (int x1, int x2, int y, int c);
-void (*bogl_vline) (int x, int y1, int y2, int c);
-void (*bogl_text) (int x, int y, const char *s, int n, int fg, int bg, int ul,
+extern void (*bogl_pixel) (int x, int y, int c);
+extern void (*bogl_hline) (int x1, int x2, int y, int c);
+extern void (*bogl_vline) (int x, int y1, int y2, int c);
+extern void (*bogl_text) (int x, int y, const char *s, int n, int fg, int bg, int ul,
 		   const struct bogl_font *font);
-void (*bogl_clear) (int x1, int y1, int x2, int y2, int c);
-void (*bogl_move) (int sx, int sy, int dx, int dy, int w, int h);
-void (*bogl_put) (int x, int y, const struct bogl_pixmap *pixmap,
+extern void (*bogl_clear) (int x1, int y1, int x2, int y2, int c);
+extern void (*bogl_move) (int sx, int sy, int dx, int dy, int w, int h);
+extern void (*bogl_put) (int x, int y, const struct bogl_pixmap *pixmap,
 		  const int color_map[16]);
-void (*bogl_pointer) (int visible, int x, int y,
+extern void (*bogl_pointer) (int visible, int x, int y,
 		      const struct bogl_pointer *,
 		      int colors[2]);
-void (*bogl_set_palette) (int c, int nc, const unsigned char palette[][3]);
-void (*bogl_reinit) (void);
+extern void (*bogl_set_palette) (int c, int nc, const unsigned char palette[][3]);
+extern void (*bogl_reinit) (void);
 
 #endif /* bogl_h */