--- pcm_usb_stream.c	2008-11-21 18:08:16.000000000 -0500
+++ pcm_usb_stream.c	2009-12-30 12:36:00.654452577 -0500
@@ -258,7 +258,7 @@
 	snd_pcm_us_t *us = io->private_data;
 	VDBG("%u", us->uus->s->periods_done);
 
-	if (io->stream == SND_PCM_STREAM_PLAYBACK)
+	if (io->stream == SND_PCM_STREAM_PLAYBACK && us->uus->s)
 		memset(us->uus->write_area, 0, us->uus->s->write_size);
 
 	return 0;