diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 073d85954a5..e7683cef015 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -710,7 +710,9 @@ order
 \code{st_atime},
 \code{st_mtime},
 \code{st_ctime}.
-More items may be added at the end by some implementations.
+More items may be added at the end by some implementations.  Note that
+on the Macintosh, the time values are floating point values, like all
+time values on the Macintosh.
 (On MS Windows, some items are filled with dummy values.)
 Availability: Macintosh, \UNIX{}, Windows.