diff --git a/lib/timer.js b/lib/timer.js
index <HASH>..<HASH> 100644
--- a/lib/timer.js
+++ b/lib/timer.js
@@ -125,6 +125,11 @@ timers.create(id, options, (err) => {
   create(id, body, cb) {
     const payload = body;
     const transport = this.transports[payload.callback.transport];
+    if (!transport) {
+      const err = new Error(`Unknown transport ${payload.callback.transport}`)
+      err.code = 'ENOTRANSPORT'
+      return setImmediate(cb, err)
+    }
     if ( this.has( id ) ) {
       const err = new Error(`Timer with id ${id} already exists` );
       err.code = 'EKEYEXISTS';
timer: add error handler for case when a transport isn't defined