--- squashfs-tools/read_fs.c
+++ squashfs-tools/read_fs.c
@@ -62,7 +62,7 @@ extern int add_file(int, int, unsigned i
 
 #define ERROR(s, args...)		fprintf(stderr, s, ## args)
 
-int swap;
+extern int swap;
 
 int read_block(int fd, int start, int *next, unsigned char *block, squashfs_super_block *sBlk)
 {