--- a/common/zoom.c	2020-07-05 15:50:00.625088023 +0200
+++ a/common/zoom.c	2020-07-05 15:50:11.681754613 +0200
@@ -35,7 +35,7 @@
    restore_stack(saved);
 }
 
-int boxcolor;
+extern int boxcolor;
 
 #ifndef XFRACT
 void dispbox(void)