diff --git a/check_systemd_service.sh b/check_systemd_service.sh
index a5b810f..052749e 100755
--- a/check_systemd_service.sh
+++ b/check_systemd_service.sh
@@ -12,7 +12,7 @@ IS_TIMER=false
 IS_ALLOWED_DISABLED=false
 
 # Parse command line arguments
-while getopts "u:t" opt; do
+while getopts "u:t:d" opt; do
   case ${opt} in
     u )
       UNIT_NAME=$OPTARG
@@ -20,11 +20,11 @@ while getopts "u:t" opt; do
     t )
       IS_TIMER=true
       ;;
-    t )
+    d )
       IS_ALLOWED_DISABLED=true
       ;;
     \? )
-      echo "Invalid option: $OPTARG" 1>&2
+      usage
       exit 1
       ;;
     : )