diff --git a/Doc/lib/libregsub.tex b/Doc/lib/libregsub.tex
index 4c1497cfe89..d075e99e8c1 100644
--- a/Doc/lib/libregsub.tex
+++ b/Doc/lib/libregsub.tex
@@ -49,3 +49,10 @@ pattern uses any characters except letters, digits and underscores as
 word delimiters.  Capitalization is done by changing the first
 character of each word to upper case.
 \end{funcdesc}
+
+\begin{funcdesc}{clear_cache}{}
+The regsub module maintains a cache of compiled regular expressions,
+keyed on the regular expression string and the syntax of the regex
+module at the time the expression was compiled.  This function clears
+that cache.
+\end{funcdesc}
diff --git a/Doc/libregsub.tex b/Doc/libregsub.tex
index 4c1497cfe89..d075e99e8c1 100644
--- a/Doc/libregsub.tex
+++ b/Doc/libregsub.tex
@@ -49,3 +49,10 @@ pattern uses any characters except letters, digits and underscores as
 word delimiters.  Capitalization is done by changing the first
 character of each word to upper case.
 \end{funcdesc}
+
+\begin{funcdesc}{clear_cache}{}
+The regsub module maintains a cache of compiled regular expressions,
+keyed on the regular expression string and the syntax of the regex
+module at the time the expression was compiled.  This function clears
+that cache.
+\end{funcdesc}