diff --git a/manual-of-style/index.html b/manual-of-style/index.html
index baa6bb7a..64166087 100644
--- a/manual-of-style/index.html
+++ b/manual-of-style/index.html
@@ -910,7 +910,15 @@ <h3>Punctuation</h3>
 
 <ul>
 <li>Use correct punctuation. A hard copy of [[[CHICAGO]]] [[CHICAGO]] or
-  [[[GREGG]]] [[GREGG]] may be of some help.</li>
+  [[[GREGG]]] [[GREGG]] may be of some help.
+<ul>
+	<li>Exception: Em dash
+		<ul>
+			<li>Put a space before and after an em dash.</li>
+		</ul>
+	</li>
+</ul>
+</li>
 
 <li>Remember you are typing <abbr title=
 "HyperText Markup Language">HTML</abbr> or <abbr title=