diff --git a/theory.html b/theory.html
index 298db866b..75e347f0f 100644
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+++ b/theory.html
@@ -60,7 +60,6 @@ <h2 id="scope">Scope of the <code><abbr>tz</abbr></code> database</h2>
 American mountain time zone can choose from the timezones
 <code>America/Denver</code> which observes US-style daylight saving
 time (<abbr>DST</abbr>),
-<code>America/Mazatlan</code> which observes Mexican-style <abbr>DST</abbr>,
 and <code>America/Phoenix</code> which does not observe <abbr>DST</abbr>.
 Applications that also deal with past timestamps in the mountain time
 zone can choose from over a dozen timezones, such as