diff --git a/include/extern.h b/include/extern.h
index b844fa00f..f545be56c 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -342,7 +342,7 @@ extern int wiz_debug_cmd_bury(void);
 /* ### display.c ### */
 
 extern void magic_map_background(xchar, xchar, int);
-static void map_altar(xchar, xchar, int);
+extern void map_altar(xchar, xchar, int);
 extern void map_background(xchar, xchar, int);
 extern void map_trap(struct trap *, int);
 extern void map_object(struct obj *, int);