diff --git a/run-document-server.sh b/run-document-server.sh
index 4e8fde6..6a1052a 100755
--- a/run-document-server.sh
+++ b/run-document-server.sh
@@ -71,9 +71,13 @@ read_setting(){
     "mariadb"|"mysql")
       DB_PORT=${DB_PORT:-"3306"}
       ;;
-    *)
+    "")
       DB_PORT=${DB_PORT:-${POSTGRESQL_SERVER_PORT:-$(${JSON} services.CoAuthoring.sql.dbPort)}}
       ;;
+    *)
+      echo "ERROR: unknown database type"
+      exit 1
+      ;;
   esac
   DB_NAME=${DB_NAME:-${POSTGRESQL_SERVER_DB_NAME:-$(${JSON} services.CoAuthoring.sql.dbName)}}
   DB_USER=${DB_USER:-${POSTGRESQL_SERVER_USER:-$(${JSON} services.CoAuthoring.sql.dbUser)}}