diff --git a/man/sd_bus_error.xml b/man/sd_bus_error.xml
index 38bc30311..2d6be1e5d 100644
--- a/man/sd_bus_error.xml
+++ b/man/sd_bus_error.xml
@@ -297,9 +297,10 @@ along with systemd; If not, see <http://www.gnu.org/licenses/>.
     <parameter>format</parameter> and the arguments.</para>
 
     <para><function>sd_bus_error_get_errno</function> is will convert
-    <structname>e->name</structname> to an errno-like value
-    using the same rules as <function>sd_bus_error_set</function>.
-    </para>
+    <structname>e->name</structname> to an errno-like value using the
+    same rules as <function>sd_bus_error_set</function>.  If
+    <parameter>e</parameter> is <constant>NULL</constant>, 0 will be
+    returned.</para>
 
     <para><function>sd_bus_error_copy</function> will initialize
     <parameter>dst</parameter> using the values in