diff --git a/Doc/lib/libtime.tex b/Doc/lib/libtime.tex
index 6823d5f80c9..83d520e20dd 100644
--- a/Doc/lib/libtime.tex
+++ b/Doc/lib/libtime.tex
@@ -287,7 +287,9 @@ Availability: Most modern \UNIX{} systems.
 Return the time as a floating point number expressed in seconds since
 the epoch, in UTC.  Note that even though the time is always returned
 as a floating point number, not all systems provide time with a better
-precision than 1 second.
+precision than 1 second.  While this function normally returns
+non-decreasing values, it can return a lower value than a previous
+call if the system clock has been set back between the two calls.
 \end{funcdesc}
 
 \begin{datadesc}{timezone}