diff --git a/libntfs-3g/ioctl.c b/libntfs-3g/ioctl.c
index 6c49395d..66cedaf9 100644
--- a/libntfs-3g/ioctl.c
+++ b/libntfs-3g/ioctl.c
@@ -141,7 +141,8 @@ static int fstrim_limits(ntfs_volume *vol,
 			u64 *discard_max_bytes)
 {
 	struct stat statbuf;
-	char path1[80], path2[80];
+	char path1[40]; /* holds "/sys/dev/block/%d:%d" */
+	char path2[40 + sizeof(path1)]; /* less than 40 bytes more than path1 */
 	int ret;
 
 	/* Stat the backing device.  Caller has ensured it is a block device. */
diff --git a/libntfs-3g/realpath.c b/libntfs-3g/realpath.c
index a93bc698..d56667e4 100644
--- a/libntfs-3g/realpath.c
+++ b/libntfs-3g/realpath.c
@@ -45,8 +45,8 @@ canonicalize_dm_name(const char *ptname, char *canonical)
 {
 	FILE	*f;
 	size_t	sz;
-	char	path[MAPPERNAMELTH + 24];
 	char	name[MAPPERNAMELTH + 16];
+	char	path[sizeof(name) + 16];
 	char	*res = NULL;
 
 	snprintf(path, sizeof(path), "/sys/block/%s/dm/name", ptname);