diff --git a/docs/machine_usage.xml b/docs/machine_usage.xml
index 5a9e164..6a5762e 100644
--- a/docs/machine_usage.xml
+++ b/docs/machine_usage.xml
@@ -189,7 +189,7 @@ that action.
 <dd>The University of Waterloo <a href="/">Computer Science Club</a>,
         a student chapter of the ACM.  The CSC office is located in room
         3036/3037 of Mathematics and Computer Building (UW campus),
-        telephone number (519) 888-4657 x3870.
+        telephone number (519) 888-4657 x33870.
     </dd>
 
 <dt>CSC Network</dt>