diff --git a/shell-completion/bash/systemd-cat b/shell-completion/bash/systemd-cat
index 6ccc7bf000..0d7e3d7a89 100644
--- a/shell-completion/bash/systemd-cat
+++ b/shell-completion/bash/systemd-cat
@@ -31,7 +31,7 @@ _systemd_cat() {
 
     local -A OPTS=(
         [STANDALONE]='-h --help --version'
-        [ARG]='-t --identifier -p --priority --stderr-priority --level-prefix'
+        [ARG]='-t --identifier -p --priority --stderr-priority --level-prefix --namespace'
     )
 
     _init_completion || return
@@ -47,6 +47,9 @@ _systemd_cat() {
             --level-prefix)
                 comps='yes no'
                 ;;
+            --namespace)
+                comps=$(journalctl --list-namespaces --output=cat 2>/dev/null)
+                ;;
         esac
         COMPREPLY=( $(compgen -W '$comps' -- "$cur") )
         return 0
diff --git a/shell-completion/zsh/_systemd b/shell-completion/zsh/_systemd
index 863631571e..44476144c1 100644
--- a/shell-completion/zsh/_systemd
+++ b/shell-completion/zsh/_systemd
@@ -19,6 +19,7 @@ case "$service" in
             {-t+,--identifier=}'[Set syslog identifier.]:syslog identifier:' \
             {-p+,--priority=}'[Set priority value.]:value:({0..7})' \
             '--level-prefix=[Control whether level prefix shall be parsed.]:boolean:(1 0)' \
+            '--namespace=[Connect to specified journal namespace.]:journal namespace:' \
             ':Message'
         ;;
     systemd-cgls)