diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 3662a46..631f241 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -843,12 +843,14 @@
 \end{funcdesc}
 
 \begin{funcdesc}{major}{device}
-Extracts a device major number from a raw device number.
+Extracts the device major number from a raw device number (usually
+the \member{st_dev} or \member{st_rdev} field from \ctype{stat}).
 \versionadded{2.3}
 \end{funcdesc}
 
 \begin{funcdesc}{minor}{device}
-Extracts a device minor number from a raw device number.
+Extracts the device minor number from a raw device number (usually
+the \member{st_dev} or \member{st_rdev} field from \ctype{stat}).
 \versionadded{2.3}
 \end{funcdesc}