diff --git a/CHANGELOG.md b/CHANGELOG.md
index fd2d7b4..c2df1b3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+* Display help message if mandatory arguments are missing.
+
 ### Deprecated
 
 ### Removed
diff --git a/bkctld b/bkctld
index 080bd29..21ee88d 100755
--- a/bkctld
+++ b/bkctld
@@ -52,17 +52,30 @@ case "${subcommand}" in
     ;;
     "init" | "is-on")
         jail_name="${2:-}"
-        "${LIBDIR}/bkctld-${subcommand}" "${jail_name}"
+        if [ -z "${jail_name}" ]; then
+            "${LIBDIR}/bkctld-help"
+            exit 1
+        else
+            "${LIBDIR}/bkctld-${subcommand}" "${jail_name}" 
+        fi
     ;;
     "key" | "port" | "ip")
         jail_name="${2:-}"
         option="${3:-}"
-        "${LIBDIR}/bkctld-${subcommand}" "${jail_name}" "${option}"
+        if [ "${jail_name}" = "all" ] || [ -z "${jail_name}" ]; then
+            "${LIBDIR}/bkctld-help"
+            exit 1
+        else
+            "${LIBDIR}/bkctld-${subcommand}" "${jail_name}" "${option}"
+        fi
     ;;
     "start" | "stop" | "reload" | "restart" | "sync" | "update" | "remove" | "firewall")
         jail_name="${2:-}"
         if [ "${jail_name}" = "all" ]; then
             "${LIBDIR}/bkctld-list" | xargs --no-run-if-empty --max-args=1 --max-procs=0 "${LIBDIR}/bkctld-${subcommand}"
+        elif [ -z "${jail_name}" ]; then
+            "${LIBDIR}/bkctld-help"
+            exit 1
         else
             "${LIBDIR}/bkctld-${subcommand}" "${jail_name}"
         fi