diff --git a/changes/bug10470 b/changes/bug10470
new file mode 100644
index 0000000000..2b753436d9
--- /dev/null
+++ b/changes/bug10470
@@ -0,0 +1,4 @@
+  o Documentation fixes:
+    - Note that all but one DirPort entry must have the NoAdvertise flag
+      set. Fix for #10470.
+
diff --git a/doc/tor.1.txt b/doc/tor.1.txt
index 34a9f24eb6..28e7c5d7d1 100644
--- a/doc/tor.1.txt
+++ b/doc/tor.1.txt
@@ -1799,7 +1799,8 @@ if DirPort is non-zero):
 [[DirPort]] **DirPort** \['address':]__PORT__|**auto** [_flags_]::
     If this option is nonzero, advertise the directory service on this port.
     Set it to "auto" to have Tor pick a port for you.  This option can occur
-    more than once. (Default: 0)
+    more than once, but only one advertised DirPort is supported: all
+    but one DirPort must have the **NoAdvertise** flag set. (Default: 0)
 +
     The same flags are supported here as are supported by ORPort.