diff --git a/man/systemctl.xml b/man/systemctl.xml
index a966e3ea7a..d98a89341a 100644
--- a/man/systemctl.xml
+++ b/man/systemctl.xml
@@ -558,7 +558,7 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
           <term><command>clean <replaceable>PATTERN</replaceable>…</command></term>
 
           <listitem>
-            <para>Remove the configuration, state, cache, logs or runtime data of the specified units. Use
+            <para>Remove the configuration, state, cache, logs, runtime or file descriptor store data of the specified units. Use
             <option>--what=</option> to select which kind of resource to remove. For service units this may
             be used to remove the directories configured with <varname>ConfigurationDirectory=</varname>,
             <varname>StateDirectory=</varname>, <varname>CacheDirectory=</varname>,
@@ -573,7 +573,8 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
             command only applies to units that use either of these settings. If <option>--what=</option> is
             not specified, the cache and runtime data as well as the file descriptor store are removed (as
             these three types of resources are generally redundant and reproducible on the next invocation of
-            the unit). Note that the specified units must be stopped to invoke this operation.</para>
+            the unit). Multiple values can be seperated by commas. Note that the specified units must be stopped
+            to invoke this operation.</para>
 
             <table>
               <title>
@@ -616,6 +617,10 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
                     <entry><literal>all</literal></entry>
                     <entry>All of the above</entry>
                   </row>
+                  <row>
+                    <entry><literal>help</literal></entry>
+                    <entry>Show the supported values and exit</entry>
+                  </row>
                 </tbody>
               </tgroup>
             </table>
diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c
index 3c691c5dee..d1e3340737 100644
--- a/src/systemctl/systemctl.c
+++ b/src/systemctl/systemctl.c
@@ -965,7 +965,7 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
 
                 case ARG_WHAT:
                         if (isempty(optarg))
-                                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "--what= requires arguments.");
+                                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "--what= requires arguments (see --what=help).");
 
                         for (const char *p = optarg;;) {
                                 _cleanup_free_ char *k = NULL;
@@ -982,7 +982,8 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
                                              "cache\n"
                                              "logs\n"
                                              "configuration\n"
-                                             "fdstore");
+                                             "fdstore\n"
+                                             "all");
                                         return 0;
                                 }