diff --git a/introspection/nm-manager.xml b/introspection/nm-manager.xml
index ee84a47b0..1bb76d09f 100644
--- a/introspection/nm-manager.xml
+++ b/introspection/nm-manager.xml
@@ -226,7 +226,8 @@
           related to that domain.  Available domains are: [NONE, HW, RFKILL,
           ETHER, WIFI, BT, MB, DHCP4, DHCP6, PPP, WIFI_SCAN, IP4, IP6, AUTOIP4,
           DNS, VPN, SHARING, SUPPLICANT, USER_SET, SYS_SET, SUSPEND, CORE,
-          DEVICE, OLPC]
+          DEVICE, OLPC].  If an empty string is given, the log level is changed
+          but the current set of log domains remains unchanged.
         </tp:docstring>
       </arg>
     </method>