diff -upr btrfs-progs-v4.3.1.orig/utils.c btrfs-progs-v4.3.1/utils.c
--- btrfs-progs-v4.3.1.orig/utils.c	2015-11-20 01:15:32.227019383 +0100
+++ btrfs-progs-v4.3.1/utils.c	2015-11-20 01:16:59.419971215 +0100
@@ -1208,13 +1208,19 @@ static int resolve_loop_device(const cha
 {
 	int ret;
 	FILE *f;
+	struct stat stat_buf;
 	char fmt[20];
 	char p[PATH_MAX];
 	char real_loop_dev[PATH_MAX];
 
 	if (!realpath(loop_dev, real_loop_dev))
 		return -errno;
-	snprintf(p, PATH_MAX, "/sys/block/%s/loop/backing_file", strrchr(real_loop_dev, '/'));
+
+	if (stat(real_loop_dev, &stat_buf) || !S_ISBLK(stat_buf.st_mode))
+		return -errno;
+
+	snprintf(p, PATH_MAX, "/sys/dev/block/%d:%d/loop/backing_file",
+		major(stat_buf.st_rdev), minor(stat_buf.st_rdev));
 	if (!(f = fopen(p, "r"))) {
 		if (errno == ENOENT)
 			/*