--- squashfs-tools/mksquashfs.c
+++ squashfs-tools/mksquashfs.c
@@ -3588,6 +3588,9 @@
 	int readb_mbytes = READER_BUFFER_DEFAULT, writeb_mbytes = WRITER_BUFFER_DEFAULT, fragmentb_mbytes = FRAGMENT_BUFFER_DEFAULT;
 	int s_minor;
 
+	/* set struct sBlk to zero */
+	memset(&sBlk, 0, sizeof (sBlk));
+
 #if __BYTE_ORDER == __BIG_ENDIAN
 	be = TRUE;
 #else