diff --git a/README.md b/README.md
index a01bc90..0185e8b 100644
--- a/README.md
+++ b/README.md
@@ -1,28 +1,38 @@
 # Usage
 
 ```
-nft-edit-ruleset [--config [CONFIG_FILE]] [--fail] [--timeout SECONDS] [--yes]
+nft-edit-ruleset [--config [CONFIG_FILE]] [--fail] [--timeout SECONDS] [--yes] 
 ```
 
 # Description
 
-Interactively edit the current nftables ruleset using the editor specified
-by environment variable EDITOR (defaulting to vim). Optionally, revert
-changes after a timeout given in seconds.
+Interactively edit the current nftables ruleset using the editor specified by
+environment variable EDITOR (defaulting to vim). Optionally, revert changes
+after a timeout given in seconds.
 
 # Options
 
-- `-c`, `--config [CONFIG_FILE]`: On successfully applying the
- changes, save ruleset to `CONFIG_FILE` (default: /etc/nftables.conf).
-- `-f`, `--fail`: Exit unsuccessfully if changes fail to apply.
-- `-h`, `--help`: Display this message and exit.
-- `-t NUM`, `--timeout NUM`: Revert changes after NUM seconds.
-- `-y`, `--yes`: No confirmation before applying changes.
+- `-c`, `--config [CONFIG_FILE]`:  
+  If set, on successfully applying changes, save the resulting ruleset to
+  `CONFIG_FILE` (if `CONFIG_FILE` is not specified, it defaults to
+  /etc/nftables.conf).  
+  This option is mutually exclusive with option `--timeout`.
+- `-f`, `--fail`:  
+  Exit on changes failing to apply instead of prompting the user for re-edit.
+- `-h`, `--help`:  
+  Display this message and exit.
+- `-t NUM`, `--timeout NUM`:  
+  Revert any changes NUM seconds after they have been applied. This is
+  implemented with a systemd timer that remains active after the program
+  has ended.  
+  This option is mutually exclusive with option `--config`.
+- `-y`, `--yes`:  
+  Do not prompt for confirmation before applying changes.
 
 # Exit Codes
 
-* 0: Success: No changes to apply or changes applied successfully.
-* 1: Error: Usage error or failed or aborted changes.
+- 0: Success: No changes to apply or changes applied successfully.
+- 1: Error: Usage error or failed or aborted changes.
 
 # Author and License
 
diff --git a/nft-edit-ruleset b/nft-edit-ruleset
index 2d2fd39..8301bc8 100755
--- a/nft-edit-ruleset
+++ b/nft-edit-ruleset
@@ -43,12 +43,24 @@ set_timeout() {
   local ruleset=$1
   local seconds=$2
 
-  systemd-run \
-    --description="Reverting nftables ruleset changes by $0 (PID=$$)" \
+  if test -z "$(command -v systemd-run)" ; then
+    echo "ERROR: Setting undo timeout failed (systemd-run not found)" >&2
+    return 1
+  fi
+
+  if systemd-run \
+    --unit="nft-edit-ruleset-revert-changes" \
+    --description="reverting nftables ruleset changes by $0 (PID=$$)" \
     --on-active="$seconds" \
     --timer-property=AccuracySec=100ms \
     --quiet \
     bash -c "nft -f '$ruleset' ; rm -f '$ruleset'"
+  then
+    return 0
+  else
+    echo "ERROR: Setting undo timeout failed (already running?)" >&2
+    return 1
+  fi
 }
 
 store_config() {
@@ -90,15 +102,21 @@ after a timeout given in seconds.
 
 # OPTIONS
 - \`-c\`, \`--config [CONFIG_FILE]\`:  
-  On success, save ruleset to \`CONFIG_FILE\` (default: $default_config_file).
+  If set, on successfully applying changes, save the resulting ruleset to
+  \`CONFIG_FILE\` (if \`CONFIG_FILE\` is not specified, it defaults to
+  $default_config_file).  
+  This option is mutually exclusive with option \`--timeout\`.
 - \`-f\`, \`--fail\`:  
-  Exit unsuccessfully if changes fail to apply.
+  Exit on changes failing to apply instead of prompting the user for re-edit.
 - \`-h\`, \`--help\`:  
   Display this message and exit.
 - \`-t NUM\`, \`--timeout NUM\`:  
-  Revert changes after NUM seconds.
+  Revert any changes NUM seconds after they have been applied. This is
+  implemented with a systemd timer that remains active after the program
+  has ended.  
+  This option is mutually exclusive with option \`--config\`.
 - \`-y\`, \`--yes\`:  
-  No confirmation before applying changes.
+  Do not prompt for confirmation before applying changes.
 
 # EXIT CODES
 - 0: Success: No changes to apply or changes applied successfully.
@@ -130,12 +148,16 @@ EOF
     -c|--config)
       config=true
 
-      if test "$#" -gt 0 && { test -w "$2" || test -w "$(dirname "$2")" ; } ; then
+      if \
+          test "$#" -gt 0 && \
+          ! [[ "$2" =~ ^- ]] && \
+          { test -w "$2" || test -w "$(dirname "$2")" ; }
+      then
         shift 1
         config_file=$1
       elif test -z "$default_config_file" ; then
         echo \
-          "ERROR: Option \`--config\` was used without an argument," \
+          "ERROR: Option \`--config\` was used without a valid argument," \
           "but no default location of a file \"nftables.conf\" could be found" \
           "(use \`--config CONFIG_FILE\` to specify a location); aborted." >&2
         exit 1
@@ -159,6 +181,11 @@ EOF
   fi
 done
 
+if "$config" && "$timeout" ; then
+  echo "ERROR: Options \`--config\` and \`--timeout\` are mutually exclusive; aborted." >&2
+  exit 1
+fi
+
 ##
 # Main Program
 
@@ -179,6 +206,8 @@ nft list ruleset >> "$tmp"
 
 cat "$tmp" > "$tmp_old"
 
+rv=0
+
 while true ; do
   editor=${EDITOR:-vim}
 
@@ -192,7 +221,8 @@ while true ; do
         echo "Stored unchanged ruleset to config_file=\"$config_file\"."
       else
         echo "ERROR: Storing unchanged ruleset to config_file=\"$config_file\" failed." >&2
-        exit 1
+        rv=1
+        break
       fi
     fi
 
@@ -207,36 +237,39 @@ while true ; do
           ;;
         *)
           echo "Aborting (user request)."
-          exit 1
+          rv=1
+          break
           ;;
       esac
     fi
 
     if ! nft -c -f "$tmp" ; then
       if "$fail" ; then
-        exit 1
+        rv=1
+        break
       else
         read -p "Errors in changes detected (Ctrl-c to abort, ENTER to continue editing)" -r answer
       fi
     elif ! nft -f "$tmp" ; then
       if "$fail" ; then
-        exit 1
+        rv=1
+        break
       else
         read -p "Errors when applying changes (Ctrl-c to abort, ENTER to continue editing)" -r answer
       fi
     else
-      if "$timeout" ; then
-        set_timeout "$tmp_old" "$timeout_secs"
-      fi
-
       echo "Changes applied successfully."
 
-      if "$config" ; then
+      if "$timeout" ; then
+        if ! set_timeout "$tmp_old" "$timeout_secs" ; then
+          rv=1
+        fi
+      elif "$config" ; then
         if store_config "$tmp" "$config_file" ; then
           echo "Stored changed ruleset to config_file=\"$config_file\"."
         else
           echo "ERROR: Storing changed ruleset to config_file=\"$config_file\" failed." >&2
-          exit 1
+          rv=1
         fi
       fi
 
@@ -245,6 +278,8 @@ while true ; do
   fi
 done
 
+exit $rv
+
 ##
 # Exit Codes
 # - 0: Success: No changes to apply or changes applied successfully.