diff --git a/doc/system_security_descriptors.txt b/doc/system_security_descriptors.txt
index f8f4aef7..2003bb46 100644
--- a/doc/system_security_descriptors.txt
+++ b/doc/system_security_descriptors.txt
@@ -1,4 +1,4 @@
-$SD attribute value for the system files:
+$SD attribute value for the system files on an NTFS 1.2 volume:
 
 $MFT, $MFTMirr, $LogFile, $AttrDef, $Bitmap, $Boot, $BadClus, and $UpCase: