diff --git a/doc/capturefrm.txt b/doc/capturefrm.txt
index bf4e720..6957250 100644
--- a/doc/capturefrm.txt
+++ b/doc/capturefrm.txt
@@ -11,13 +11,15 @@ All sniff frames follow the same format:
 	Offset	Name		Size		Description
 	--------------------------------------------------------------------
 	0	CaptureHeader			AVS capture metadata header
-	56	802.11Header	[10-30]		802.11 frame header
+	64	802.11Header	[10-30]		802.11 frame header
 	??	802.11Payload	[0-2312]	802.11 frame payload
 	??	802.11FCS	4		802.11 frame check sequence
 
 Note that the header and payload are variable length and the payload
 may be empty.
 
+If the hardware does not supply the FCS to the driver, then the frame shall
+have a FCS of 0xFFFFFFFF.
 
 3. Byte Order
 All multibyte fields of the capture header are in "network" byte