--- a/squashfs-tools/mksquashfs.c

+++ b/squashfs-tools/mksquashfs.c

@@ -2447,8 +2447,8 @@ void *frag_deflator(void *arg)

 			write_buffer->block = bytes;

 			bytes += compressed_size;

 			fragments_outstanding --;

-			pthread_mutex_unlock(&fragment_mutex);

 			queue_put(to_writer, write_buffer);

+			pthread_mutex_unlock(&fragment_mutex);

 			TRACE("Writing fragment %lld, uncompressed size %d, "

 				"compressed size %d\n", file_buffer->block,

 				file_buffer->size, compressed_size);