diff --git a/changes/bug21720 b/changes/bug21720
new file mode 100644
index 000000000..6d2fbcf71
--- /dev/null
+++ b/changes/bug21720
@@ -0,0 +1,5 @@
+  o Documentation:
+    - Update the description of the directory server options in the manual
+      page, to clarify that DirPort is no longer necessary to be a directory
+      cache.  Closes ticket 21720.
+
diff --git a/doc/tor.1.txt b/doc/tor.1.txt
index de2e2b4a0..1665cfe94 100644
--- a/doc/tor.1.txt
+++ b/doc/tor.1.txt
@@ -2121,8 +2121,9 @@ is non-zero):
 DIRECTORY SERVER OPTIONS
 ------------------------
 
-The following options are useful only for directory servers (that is,
-if DirPort is non-zero):
+The following options are useful only for directory servers. (Relays with
+enough bandwidth automatically become directory servers; see DirCache for
+details.)
 
 [[DirPortFrontPage]] **DirPortFrontPage** __FILENAME__::
     When this option is set, it takes an HTML file and publishes it as "/" on