--- a/utils.c
+++ b/utils.c
@@ -833,13 +833,19 @@
 {
 	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")))
 		return -errno;