diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index c92aa4d..6a1223f 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -1025,7 +1025,11 @@
 provided.
 \warning{Use of \function{tmpnam()} is vulnerable to symlink attacks;
 consider using \function{tmpfile()} instead.}
-Availability: \UNIX, Windows.
+Availability: \UNIX, Windows.  This function probably shouldn't be used
+on Windows, though:  Microsoft's implementation of \function{tmpnam()}
+always creates a name in the root directory of the current drive, and
+that's generally a poor location for a temp file (depending on
+privileges, you may not even be able to open a file using this name).
 \end{funcdesc}
 
 \begin{datadesc}{TMP_MAX}