--- squashfs-tools/read_fs.c
+++ squashfs-tools/read_fs.c
@@ -73,7 +73,7 @@ extern zlib_uncompress_t uncompress_fct;
 #define uncompress_fct uncompress
 #endif
 
-int swap;
+extern int swap;
 
 int read_block(int fd, long long start, long long *next, unsigned char *block, squashfs_super_block *sBlk)
 {