diff --git a/doc/scsh-manual/sre.tex b/doc/scsh-manual/sre.tex
index 1e2c3e0..b2e87cb 100644
--- a/doc/scsh-manual/sre.tex
+++ b/doc/scsh-manual/sre.tex
@@ -527,6 +527,11 @@ The rules for determining if an SRE is a simple, char-class SRE or a
 more complex SRE form a little ``type system'' for SRE's. See the summary
 section preceding this one for a complete listing of these rules.
 
+\note{There is no way to include the ASCII NUL character in a
+  character set or search for it in any other way using regular
+  expression.  This is because the POSIX regexp facility is based on
+  the C language which uses ASCII NUL to terminate strings.}
+
 \paragraph{Case sensitivity}
 
 There are three forms that control case sensitivity: